dist/ramda.js

//  Ramda v0.27.1
//  https://github.com/ramda/ramda
//  (c) 2013-2020 Scott Sauyet, Michael Hurley, and David Chambers
//  Ramda may be freely distributed under the MIT license.

(function (global, factory) {
  typeof exports === 'object' && typeof module !== 'undefined' ? factory(exports) :
  typeof define === 'function' && define.amd ? define(['exports'], factory) :
  (global = global || self, factory(global.R = {}));
}(this, function (exports) { 'use strict';

  /**
   * A function that always returns `false`. Any passed in parameters are ignored.
   *
   * @func
   * @memberOf R
   * @since v0.9.0
   * @category Function
   * @sig * -> Boolean
   * @param {*}
   * @return {Boolean}
   * @see R.T
   * @example
   *
   *      R.F(); //=> false
   */
  var F = function() {return false;};

  /**
   * A function that always returns `true`. Any passed in parameters are ignored.
   *
   * @func
   * @memberOf R
   * @since v0.9.0
   * @category Function
   * @sig * -> Boolean
   * @param {*}
   * @return {Boolean}
   * @see R.F
   * @example
   *
   *      R.T(); //=> true
   */
  var T = function() {return true;};

  /**
   * A special placeholder value used to specify "gaps" within curried functions,
   * allowing partial application of any combination of arguments, regardless of
   * their positions.
   *
   * If `g` is a curried ternary function and `_` is `R.__`, the following are
   * equivalent:
   *
   *   - `g(1, 2, 3)`
   *   - `g(_, 2, 3)(1)`
   *   - `g(_, _, 3)(1)(2)`
   *   - `g(_, _, 3)(1, 2)`
   *   - `g(_, 2, _)(1, 3)`
   *   - `g(_, 2)(1)(3)`
   *   - `g(_, 2)(1, 3)`
   *   - `g(_, 2)(_, 3)(1)`
   *
   * @name __
   * @constant
   * @memberOf R
   * @since v0.6.0
   * @category Function
   * @example
   *
   *      const greet = R.replace('{name}', R.__, 'Hello, {name}!');
   *      greet('Alice'); //=> 'Hello, Alice!'
   */
  var __ = {'@@functional/placeholder': true};

  function _isPlaceholder(a) {
    return a != null &&
           typeof a === 'object' &&
           a['@@functional/placeholder'] === true;
  }

  /**
   * Optimized internal one-arity curry function.
   *
   * @private
   * @category Function
   * @param {Function} fn The function to curry.
   * @return {Function} The curried function.
   */
  function _curry1(fn) {
    return function f1(a) {
      if (arguments.length === 0 || _isPlaceholder(a)) {
        return f1;
      } else {
        return fn.apply(this, arguments);
      }
    };
  }

  /**
   * Optimized internal two-arity curry function.
   *
   * @private
   * @category Function
   * @param {Function} fn The function to curry.
   * @return {Function} The curried function.
   */
  function _curry2(fn) {
    return function f2(a, b) {
      switch (arguments.length) {
        case 0:
          return f2;
        case 1:
          return _isPlaceholder(a)
            ? f2
            : _curry1(function(_b) { return fn(a, _b); });
        default:
          return _isPlaceholder(a) && _isPlaceholder(b)
            ? f2
            : _isPlaceholder(a)
              ? _curry1(function(_a) { return fn(_a, b); })
              : _isPlaceholder(b)
                ? _curry1(function(_b) { return fn(a, _b); })
                : fn(a, b);
      }
    };
  }

  /**
   * Adds two values.
   *
   * @func
   * @memberOf R
   * @since v0.1.0
   * @category Math
   * @sig Number -> Number -> Number
   * @param {Number} a
   * @param {Number} b
   * @return {Number}
   * @see R.subtract
   * @example
   *
   *      R.add(2, 3);       //=>  5
   *      R.add(7)(10);      //=> 17
   */
  var add = _curry2(function add(a, b) {
    return Number(a) + Number(b);
  });

  /**
   * Private `concat` function to merge two array-like objects.
   *
   * @private
   * @param {Array|Arguments} [set1=[]] An array-like object.
   * @param {Array|Arguments} [set2=[]] An array-like object.
   * @return {Array} A new, merged array.
   * @example
   *
   *      _concat([4, 5, 6], [1, 2, 3]); //=> [4, 5, 6, 1, 2, 3]
   */
  function _concat(set1, set2) {
    set1 = set1 || [];
    set2 = set2 || [];
    var idx;
    var len1 = set1.length;
    var len2 = set2.length;
    var result = [];

    idx = 0;
    while (idx < len1) {
      result[result.length] = set1[idx];
      idx += 1;
    }
    idx = 0;
    while (idx < len2) {
      result[result.length] = set2[idx];
      idx += 1;
    }
    return result;
  }

  function _arity(n, fn) {
    /* eslint-disable no-unused-vars */
    switch (n) {
      case 0: return function() { return fn.apply(this, arguments); };
      case 1: return function(a0) { return fn.apply(this, arguments); };
      case 2: return function(a0, a1) { return fn.apply(this, arguments); };
      case 3: return function(a0, a1, a2) { return fn.apply(this, arguments); };
      case 4: return function(a0, a1, a2, a3) { return fn.apply(this, arguments); };
      case 5: return function(a0, a1, a2, a3, a4) { return fn.apply(this, arguments); };
      case 6: return function(a0, a1, a2, a3, a4, a5) { return fn.apply(this, arguments); };
      case 7: return function(a0, a1, a2, a3, a4, a5, a6) { return fn.apply(this, arguments); };
      case 8: return function(a0, a1, a2, a3, a4, a5, a6, a7) { return fn.apply(this, arguments); };
      case 9: return function(a0, a1, a2, a3, a4, a5, a6, a7, a8) { return fn.apply(this, arguments); };
      case 10: return function(a0, a1, a2, a3, a4, a5, a6, a7, a8, a9) { return fn.apply(this, arguments); };
      default: throw new Error('First argument to _arity must be a non-negative integer no greater than ten');
    }
  }

  /**
   * Internal curryN function.
   *
   * @private
   * @category Function
   * @param {Number} length The arity of the curried function.
   * @param {Array} received An array of arguments received thus far.
   * @param {Function} fn The function to curry.
   * @return {Function} The curried function.
   */
  function _curryN(length, received, fn) {
    return function() {
      var combined = [];
      var argsIdx = 0;
      var left = length;
      var combinedIdx = 0;
      while (combinedIdx < received.length || argsIdx < arguments.length) {
        var result;
        if (combinedIdx < received.length &&
            (!_isPlaceholder(received[combinedIdx]) ||
             argsIdx >= arguments.length)) {
          result = received[combinedIdx];
        } else {
          result = arguments[argsIdx];
          argsIdx += 1;
        }
        combined[combinedIdx] = result;
        if (!_isPlaceholder(result)) {
          left -= 1;
        }
        combinedIdx += 1;
      }
      return left <= 0
        ? fn.apply(this, combined)
        : _arity(left, _curryN(length, combined, fn));
    };
  }

  /**
   * Returns a curried equivalent of the provided function, with the specified
   * arity. The curried function has two unusual capabilities. First, its
   * arguments needn't be provided one at a time. If `g` is `R.curryN(3, f)`, the
   * following are equivalent:
   *
   *   - `g(1)(2)(3)`
   *   - `g(1)(2, 3)`
   *   - `g(1, 2)(3)`
   *   - `g(1, 2, 3)`
   *
   * Secondly, the special placeholder value [`R.__`](#__) may be used to specify
   * "gaps", allowing partial application of any combination of arguments,
   * regardless of their positions. If `g` is as above and `_` is [`R.__`](#__),
   * the following are equivalent:
   *
   *   - `g(1, 2, 3)`
   *   - `g(_, 2, 3)(1)`
   *   - `g(_, _, 3)(1)(2)`
   *   - `g(_, _, 3)(1, 2)`
   *   - `g(_, 2)(1)(3)`
   *   - `g(_, 2)(1, 3)`
   *   - `g(_, 2)(_, 3)(1)`
   *
   * @func
   * @memberOf R
   * @since v0.5.0
   * @category Function
   * @sig Number -> (* -> a) -> (* -> a)
   * @param {Number} length The arity for the returned function.
   * @param {Function} fn The function to curry.
   * @return {Function} A new, curried function.
   * @see R.curry
   * @example
   *
   *      const sumArgs = (...args) => R.sum(args);
   *
   *      const curriedAddFourNumbers = R.curryN(4, sumArgs);
   *      const f = curriedAddFourNumbers(1, 2);
   *      const g = f(3);
   *      g(4); //=> 10
   */
  var curryN = _curry2(function curryN(length, fn) {
    if (length === 1) {
      return _curry1(fn);
    }
    return _arity(length, _curryN(length, [], fn));
  });

  /**
   * Creates a new list iteration function from an existing one by adding two new
   * parameters to its callback function: the current index, and the entire list.
   *
   * This would turn, for instance, [`R.map`](#map) function into one that
   * more closely resembles `Array.prototype.map`. Note that this will only work
   * for functions in which the iteration callback function is the first
   * parameter, and where the list is the last parameter. (This latter might be
   * unimportant if the list parameter is not used.)
   *
   * @func
   * @memberOf R
   * @since v0.15.0
   * @category Function
   * @category List
   * @sig ((a ... -> b) ... -> [a] -> *) -> ((a ..., Int, [a] -> b) ... -> [a] -> *)
   * @param {Function} fn A list iteration function that does not pass index or list to its callback
   * @return {Function} An altered list iteration function that passes (item, index, list) to its callback
   * @example
   *
   *      const mapIndexed = R.addIndex(R.map);
   *      mapIndexed((val, idx) => idx + '-' + val, ['f', 'o', 'o', 'b', 'a', 'r']);
   *      //=> ['0-f', '1-o', '2-o', '3-b', '4-a', '5-r']
   */
  var addIndex = _curry1(function addIndex(fn) {
    return curryN(fn.length, function() {
      var idx = 0;
      var origFn = arguments[0];
      var list = arguments[arguments.length - 1];
      var args = Array.prototype.slice.call(arguments, 0);
      args[0] = function() {
        var result = origFn.apply(this, _concat(arguments, [idx, list]));
        idx += 1;
        return result;
      };
      return fn.apply(this, args);
    });
  });

  /**
   * Optimized internal three-arity curry function.
   *
   * @private
   * @category Function
   * @param {Function} fn The function to curry.
   * @return {Function} The curried function.
   */
  function _curry3(fn) {
    return function f3(a, b, c) {
      switch (arguments.length) {
        case 0:
          return f3;
        case 1:
          return _isPlaceholder(a)
            ? f3
            : _curry2(function(_b, _c) { return fn(a, _b, _c); });
        case 2:
          return _isPlaceholder(a) && _isPlaceholder(b)
            ? f3
            : _isPlaceholder(a)
              ? _curry2(function(_a, _c) { return fn(_a, b, _c); })
              : _isPlaceholder(b)
                ? _curry2(function(_b, _c) { return fn(a, _b, _c); })
                : _curry1(function(_c) { return fn(a, b, _c); });
        default:
          return _isPlaceholder(a) && _isPlaceholder(b) && _isPlaceholder(c)
            ? f3
            : _isPlaceholder(a) && _isPlaceholder(b)
              ? _curry2(function(_a, _b) { return fn(_a, _b, c); })
              : _isPlaceholder(a) && _isPlaceholder(c)
                ? _curry2(function(_a, _c) { return fn(_a, b, _c); })
                : _isPlaceholder(b) && _isPlaceholder(c)
                  ? _curry2(function(_b, _c) { return fn(a, _b, _c); })
                  : _isPlaceholder(a)
                    ? _curry1(function(_a) { return fn(_a, b, c); })
                    : _isPlaceholder(b)
                      ? _curry1(function(_b) { return fn(a, _b, c); })
                      : _isPlaceholder(c)
                        ? _curry1(function(_c) { return fn(a, b, _c); })
                        : fn(a, b, c);
      }
    };
  }

  /**
   * Applies a function to the value at the given index of an array, returning a
   * new copy of the array with the element at the given index replaced with the
   * result of the function application.
   *
   * @func
   * @memberOf R
   * @since v0.14.0
   * @category List
   * @sig Number -> (a -> a) -> [a] -> [a]
   * @param {Number} idx The index.
   * @param {Function} fn The function to apply.
   * @param {Array|Arguments} list An array-like object whose value
   *        at the supplied index will be replaced.
   * @return {Array} A copy of the supplied array-like object with
   *         the element at index `idx` replaced with the value
   *         returned by applying `fn` to the existing element.
   * @see R.update
   * @example
   *
   *      R.adjust(1, R.toUpper, ['a', 'b', 'c', 'd']);      //=> ['a', 'B', 'c', 'd']
   *      R.adjust(-1, R.toUpper, ['a', 'b', 'c', 'd']);     //=> ['a', 'b', 'c', 'D']
   * @symb R.adjust(-1, f, [a, b]) = [a, f(b)]
   * @symb R.adjust(0, f, [a, b]) = [f(a), b]
   */
  var adjust = _curry3(function adjust(idx, fn, list) {
    if (idx >= list.length || idx < -list.length) {
      return list;
    }
    var start = idx < 0 ? list.length : 0;
    var _idx = start + idx;
    var _list = _concat(list);
    _list[_idx] = fn(list[_idx]);
    return _list;
  });

  /**
   * Tests whether or not an object is an array.
   *
   * @private
   * @param {*} val The object to test.
   * @return {Boolean} `true` if `val` is an array, `false` otherwise.
   * @example
   *
   *      _isArray([]); //=> true
   *      _isArray(null); //=> false
   *      _isArray({}); //=> false
   */
  var _isArray = Array.isArray || function _isArray(val) {
    return (val != null &&
            val.length >= 0 &&
            Object.prototype.toString.call(val) === '[object Array]');
  };

  function _isTransformer(obj) {
    return obj != null && typeof obj['@@transducer/step'] === 'function';
  }

  /**
   * Returns a function that dispatches with different strategies based on the
   * object in list position (last argument). If it is an array, executes [fn].
   * Otherwise, if it has a function with one of the given method names, it will
   * execute that function (functor case). Otherwise, if it is a transformer,
   * uses transducer [xf] to return a new transformer (transducer case).
   * Otherwise, it will default to executing [fn].
   *
   * @private
   * @param {Array} methodNames properties to check for a custom implementation
   * @param {Function} xf transducer to initialize if object is transformer
   * @param {Function} fn default ramda implementation
   * @return {Function} A function that dispatches on object in list position
   */
  function _dispatchable(methodNames, xf, fn) {
    return function() {
      if (arguments.length === 0) {
        return fn();
      }
      var args = Array.prototype.slice.call(arguments, 0);
      var obj = args.pop();
      if (!_isArray(obj)) {
        var idx = 0;
        while (idx < methodNames.length) {
          if (typeof obj[methodNames[idx]] === 'function') {
            return obj[methodNames[idx]].apply(obj, args);
          }
          idx += 1;
        }
        if (_isTransformer(obj)) {
          var transducer = xf.apply(null, args);
          return transducer(obj);
        }
      }
      return fn.apply(this, arguments);
    };
  }

  function _reduced(x) {
    return x && x['@@transducer/reduced'] ? x :
      {
        '@@transducer/value': x,
        '@@transducer/reduced': true
      };
  }

  var _xfBase = {
    init: function() {
      return this.xf['@@transducer/init']();
    },
    result: function(result) {
      return this.xf['@@transducer/result'](result);
    }
  };

  function XAll(f, xf) {
    this.xf = xf;
    this.f = f;
    this.all = true;
  }
  XAll.prototype['@@transducer/init'] = _xfBase.init;
  XAll.prototype['@@transducer/result'] = function(result) {
    if (this.all) {
      result = this.xf['@@transducer/step'](result, true);
    }
    return this.xf['@@transducer/result'](result);
  };
  XAll.prototype['@@transducer/step'] = function(result, input) {
    if (!this.f(input)) {
      this.all = false;
      result = _reduced(this.xf['@@transducer/step'](result, false));
    }
    return result;
  };

  var _xall = _curry2(function _xall(f, xf) { return new XAll(f, xf); });

  /**
   * Returns `true` if all elements of the list match the predicate, `false` if
   * there are any that don't.
   *
   * Dispatches to the `all` method of the second argument, if present.
   *
   * Acts as a transducer if a transformer is given in list position.
   *
   * @func
   * @memberOf R
   * @since v0.1.0
   * @category List
   * @sig (a -> Boolean) -> [a] -> Boolean
   * @param {Function} fn The predicate function.
   * @param {Array} list The array to consider.
   * @return {Boolean} `true` if the predicate is satisfied by every element, `false`
   *         otherwise.
   * @see R.any, R.none, R.transduce
   * @example
   *
   *      const equals3 = R.equals(3);
   *      R.all(equals3)([3, 3, 3, 3]); //=> true
   *      R.all(equals3)([3, 3, 1, 3]); //=> false
   */
  var all = _curry2(_dispatchable(['all'], _xall, function all(fn, list) {
    var idx = 0;
    while (idx < list.length) {
      if (!fn(list[idx])) {
        return false;
      }
      idx += 1;
    }
    return true;
  }));

  /**
   * Returns the larger of its two arguments.
   *
   * @func
   * @memberOf R
   * @since v0.1.0
   * @category Relation
   * @sig Ord a => a -> a -> a
   * @param {*} a
   * @param {*} b
   * @return {*}
   * @see R.maxBy, R.min
   * @example
   *
   *      R.max(789, 123); //=> 789
   *      R.max('a', 'b'); //=> 'b'
   */
  var max = _curry2(function max(a, b) { return b > a ? b : a; });

  function _map(fn, functor) {
    var idx = 0;
    var len = functor.length;
    var result = Array(len);
    while (idx < len) {
      result[idx] = fn(functor[idx]);
      idx += 1;
    }
    return result;
  }

  function _isString(x) {
    return Object.prototype.toString.call(x) === '[object String]';
  }

  /**
   * Tests whether or not an object is similar to an array.
   *
   * @private
   * @category Type
   * @category List
   * @sig * -> Boolean
   * @param {*} x The object to test.
   * @return {Boolean} `true` if `x` has a numeric length property and extreme indices defined; `false` otherwise.
   * @example
   *
   *      _isArrayLike([]); //=> true
   *      _isArrayLike(true); //=> false
   *      _isArrayLike({}); //=> false
   *      _isArrayLike({length: 10}); //=> false
   *      _isArrayLike({0: 'zero', 9: 'nine', length: 10}); //=> true
   */
  var _isArrayLike = _curry1(function isArrayLike(x) {
    if (_isArray(x)) { return true; }
    if (!x) { return false; }
    if (typeof x !== 'object') { return false; }
    if (_isString(x)) { return false; }
    if (x.nodeType === 1) { return !!x.length; }
    if (x.length === 0) { return true; }
    if (x.length > 0) {
      return x.hasOwnProperty(0) && x.hasOwnProperty(x.length - 1);
    }
    return false;
  });

  function XWrap(fn) {
    this.f = fn;
  }
  XWrap.prototype['@@transducer/init'] = function() {
    throw new Error('init not implemented on XWrap');
  };
  XWrap.prototype['@@transducer/result'] = function(acc) { return acc; };
  XWrap.prototype['@@transducer/step'] = function(acc, x) {
    return this.f(acc, x);
  };

  function _xwrap(fn) { return new XWrap(fn); }

  /**
   * Creates a function that is bound to a context.
   * Note: `R.bind` does not provide the additional argument-binding capabilities of
   * [Function.prototype.bind](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function/bind).
   *
   * @func
   * @memberOf R
   * @since v0.6.0
   * @category Function
   * @category Object
   * @sig (* -> *) -> {*} -> (* -> *)
   * @param {Function} fn The function to bind to context
   * @param {Object} thisObj The context to bind `fn` to
   * @return {Function} A function that will execute in the context of `thisObj`.
   * @see R.partial
   * @example
   *
   *      const log = R.bind(console.log, console);
   *      R.pipe(R.assoc('a', 2), R.tap(log), R.assoc('a', 3))({a: 1}); //=> {a: 3}
   *      // logs {a: 2}
   * @symb R.bind(f, o)(a, b) = f.call(o, a, b)
   */
  var bind = _curry2(function bind(fn, thisObj) {
    return _arity(fn.length, function() {
      return fn.apply(thisObj, arguments);
    });
  });

  function _arrayReduce(xf, acc, list) {
    var idx = 0;
    var len = list.length;
    while (idx < len) {
      acc = xf['@@transducer/step'](acc, list[idx]);
      if (acc && acc['@@transducer/reduced']) {
        acc = acc['@@transducer/value'];
        break;
      }
      idx += 1;
    }
    return xf['@@transducer/result'](acc);
  }

  function _iterableReduce(xf, acc, iter) {
    var step = iter.next();
    while (!step.done) {
      acc = xf['@@transducer/step'](acc, step.value);
      if (acc && acc['@@transducer/reduced']) {
        acc = acc['@@transducer/value'];
        break;
      }
      step = iter.next();
    }
    return xf['@@transducer/result'](acc);
  }

  function _methodReduce(xf, acc, obj, methodName) {
    return xf['@@transducer/result'](obj[methodName](bind(xf['@@transducer/step'], xf), acc));
  }

  var symIterator = (typeof Symbol !== 'undefined') ? Symbol.iterator : '@@iterator';

  function _reduce(fn, acc, list) {
    if (typeof fn === 'function') {
      fn = _xwrap(fn);
    }
    if (_isArrayLike(list)) {
      return _arrayReduce(fn, acc, list);
    }
    if (typeof list['fantasy-land/reduce'] === 'function') {
      return _methodReduce(fn, acc, list, 'fantasy-land/reduce');
    }
    if (list[symIterator] != null) {
      return _iterableReduce(fn, acc, list[symIterator]());
    }
    if (typeof list.next === 'function') {
      return _iterableReduce(fn, acc, list);
    }
    if (typeof list.reduce === 'function') {
      return _methodReduce(fn, acc, list, 'reduce');
    }

    throw new TypeError('reduce: list must be array or iterable');
  }

  function XMap(f, xf) {
    this.xf = xf;
    this.f = f;
  }
  XMap.prototype['@@transducer/init'] = _xfBase.init;
  XMap.prototype['@@transducer/result'] = _xfBase.result;
  XMap.prototype['@@transducer/step'] = function(result, input) {
    return this.xf['@@transducer/step'](result, this.f(input));
  };

  var _xmap = _curry2(function _xmap(f, xf) { return new XMap(f, xf); });

  function _has(prop, obj) {
    return Object.prototype.hasOwnProperty.call(obj, prop);
  }

  var toString = Object.prototype.toString;
  var _isArguments = (function() {
    return toString.call(arguments) === '[object Arguments]' ?
      function _isArguments(x) { return toString.call(x) === '[object Arguments]'; } :
      function _isArguments(x) { return _has('callee', x); };
  }());

  // cover IE < 9 keys issues
  var hasEnumBug = !({toString: null}).propertyIsEnumerable('toString');
  var nonEnumerableProps = [
    'constructor', 'valueOf', 'isPrototypeOf', 'toString',
    'propertyIsEnumerable', 'hasOwnProperty', 'toLocaleString'
  ];
  // Safari bug
  var hasArgsEnumBug = (function() {
    return arguments.propertyIsEnumerable('length');
  }());

  var contains = function contains(list, item) {
    var idx = 0;
    while (idx < list.length) {
      if (list[idx] === item) {
        return true;
      }
      idx += 1;
    }
    return false;
  };

  /**
   * Returns a list containing the names of all the enumerable own properties of
   * the supplied object.
   * Note that the order of the output array is not guaranteed to be consistent
   * across different JS platforms.
   *
   * @func
   * @memberOf R
   * @since v0.1.0
   * @category Object
   * @sig {k: v} -> [k]
   * @param {Object} obj The object to extract properties from
   * @return {Array} An array of the object's own properties.
   * @see R.keysIn, R.values
   * @example
   *
   *      R.keys({a: 1, b: 2, c: 3}); //=> ['a', 'b', 'c']
   */
  var keys = typeof Object.keys === 'function' && !hasArgsEnumBug ?
    _curry1(function keys(obj) {
      return Object(obj) !== obj ? [] : Object.keys(obj);
    }) :
    _curry1(function keys(obj) {
      if (Object(obj) !== obj) {
        return [];
      }
      var prop, nIdx;
      var ks = [];
      var checkArgsLength = hasArgsEnumBug && _isArguments(obj);
      for (prop in obj) {
        if (_has(prop, obj) && (!checkArgsLength || prop !== 'length')) {
          ks[ks.length] = prop;
        }
      }
      if (hasEnumBug) {
        nIdx = nonEnumerableProps.length - 1;
        while (nIdx >= 0) {
          prop = nonEnumerableProps[nIdx];
          if (_has(prop, obj) && !contains(ks, prop)) {
            ks[ks.length] = prop;
          }
          nIdx -= 1;
        }
      }
      return ks;
    });

  /**
   * Takes a function and
   * a [functor](https://github.com/fantasyland/fantasy-land#functor),
   * applies the function to each of the functor's values, and returns
   * a functor of the same shape.
   *
   * Ramda provides suitable `map` implementations for `Array` and `Object`,
   * so this function may be applied to `[1, 2, 3]` or `{x: 1, y: 2, z: 3}`.
   *
   * Dispatches to the `map` method of the second argument, if present.
   *
   * Acts as a transducer if a transformer is given in list position.
   *
   * Also treats functions as functors and will compose them together.
   *
   * @func
   * @memberOf R
   * @since v0.1.0
   * @category List
   * @sig Functor f => (a -> b) -> f a -> f b
   * @param {Function} fn The function to be called on every element of the input `list`.
   * @param {Array} list The list to be iterated over.
   * @return {Array} The new list.
   * @see R.transduce, R.addIndex
   * @example
   *
   *      const double = x => x * 2;
   *
   *      R.map(double, [1, 2, 3]); //=> [2, 4, 6]
   *
   *      R.map(double, {x: 1, y: 2, z: 3}); //=> {x: 2, y: 4, z: 6}
   * @symb R.map(f, [a, b]) = [f(a), f(b)]
   * @symb R.map(f, { x: a, y: b }) = { x: f(a), y: f(b) }
   * @symb R.map(f, functor_o) = functor_o.map(f)
   */
  var map = _curry2(_dispatchable(['fantasy-land/map', 'map'], _xmap, function map(fn, functor) {
    switch (Object.prototype.toString.call(functor)) {
      case '[object Function]':
        return curryN(functor.length, function() {
          return fn.call(this, functor.apply(this, arguments));
        });
      case '[object Object]':
        return _reduce(function(acc, key) {
          acc[key] = fn(functor[key]);
          return acc;
        }, {}, keys(functor));
      default:
        return _map(fn, functor);
    }
  }));

  /**
   * Determine if the passed argument is an integer.
   *
   * @private
   * @param {*} n
   * @category Type
   * @return {Boolean}
   */
  var _isInteger = Number.isInteger || function _isInteger(n) {
    return (n << 0) === n;
  };

  /**
   * Returns the nth element of the given list or string. If n is negative the
   * element at index length + n is returned.
   *
   * @func
   * @memberOf R
   * @since v0.1.0
   * @category List
   * @sig Number -> [a] -> a | Undefined
   * @sig Number -> String -> String
   * @param {Number} offset
   * @param {*} list
   * @return {*}
   * @example
   *
   *      const list = ['foo', 'bar', 'baz', 'quux'];
   *      R.nth(1, list); //=> 'bar'
   *      R.nth(-1, list); //=> 'quux'
   *      R.nth(-99, list); //=> undefined
   *
   *      R.nth(2, 'abc'); //=> 'c'
   *      R.nth(3, 'abc'); //=> ''
   * @symb R.nth(-1, [a, b, c]) = c
   * @symb R.nth(0, [a, b, c]) = a
   * @symb R.nth(1, [a, b, c]) = b
   */
  var nth = _curry2(function nth(offset, list) {
    var idx = offset < 0 ? list.length + offset : offset;
    return _isString(list) ? list.charAt(idx) : list[idx];
  });

  /**
   * Retrieves the values at given paths of an object.
   *
   * @func
   * @memberOf R
   * @since v0.27.1
   * @category Object
   * @typedefn Idx = [String | Int]
   * @sig [Idx] -> {a} -> [a | Undefined]
   * @param {Array} pathsArray The array of paths to be fetched.
   * @param {Object} obj The object to retrieve the nested properties from.
   * @return {Array} A list consisting of values at paths specified by "pathsArray".
   * @see R.path
   * @example
   *
   *      R.paths([['a', 'b'], ['p', 0, 'q']], {a: {b: 2}, p: [{q: 3}]}); //=> [2, 3]
   *      R.paths([['a', 'b'], ['p', 'r']], {a: {b: 2}, p: [{q: 3}]}); //=> [2, undefined]
   */
  var paths = _curry2(function paths(pathsArray, obj) {
    return pathsArray.map(function(paths) {
      var val = obj;
      var idx = 0;
      var p;
      while (idx < paths.length) {
        if (val == null) {
          return;
        }
        p = paths[idx];
        val = _isInteger(p) ? nth(p, val) : val[p];
        idx += 1;
      }
      return val;
    });
  });

  /**
   * Retrieve the value at a given path.
   *
   * @func
   * @memberOf R
   * @since v0.2.0
   * @category Object
   * @typedefn Idx = String | Int
   * @sig [Idx] -> {a} -> a | Undefined
   * @param {Array} path The path to use.
   * @param {Object} obj The object to retrieve the nested property from.
   * @return {*} The data at `path`.
   * @see R.prop, R.nth
   * @example
   *
   *      R.path(['a', 'b'], {a: {b: 2}}); //=> 2
   *      R.path(['a', 'b'], {c: {b: 2}}); //=> undefined
   *      R.path(['a', 'b', 0], {a: {b: [1, 2, 3]}}); //=> 1
   *      R.path(['a', 'b', -2], {a: {b: [1, 2, 3]}}); //=> 2
   */

  var path = _curry2(function path(pathAr, obj) {
    return paths([pathAr], obj)[0];
  });

  /**
   * Returns a function that when supplied an object returns the indicated
   * property of that object, if it exists.
   *
   * @func
   * @memberOf R
   * @since v0.1.0
   * @category Object
   * @typedefn Idx = String | Int
   * @sig Idx -> {s: a} -> a | Undefined
   * @param {String|Number} p The property name or array index
   * @param {Object} obj The object to query
   * @return {*} The value at `obj.p`.
   * @see R.path, R.nth
   * @example
   *
   *      R.prop('x', {x: 100}); //=> 100
   *      R.prop('x', {}); //=> undefined
   *      R.prop(0, [100]); //=> 100
   *      R.compose(R.inc, R.prop('x'))({ x: 3 }) //=> 4
   */

  var prop = _curry2(function prop(p, obj) { return path([p], obj); });

  /**
   * Returns a new list by plucking the same named property off all objects in
   * the list supplied.
   *
   * `pluck` will work on
   * any [functor](https://github.com/fantasyland/fantasy-land#functor) in
   * addition to arrays, as it is equivalent to `R.map(R.prop(k), f)`.
   *
   * @func
   * @memberOf R
   * @since v0.1.0
   * @category List
   * @sig Functor f => k -> f {k: v} -> f v
   * @param {Number|String} key The key name to pluck off of each object.
   * @param {Array} f The array or functor to consider.
   * @return {Array} The list of values for the given key.
   * @see R.props
   * @example
   *
   *      var getAges = R.pluck('age');
   *      getAges([{name: 'fred', age: 29}, {name: 'wilma', age: 27}]); //=> [29, 27]
   *
   *      R.pluck(0, [[1, 2], [3, 4]]);               //=> [1, 3]
   *      R.pluck('val', {a: {val: 3}, b: {val: 5}}); //=> {a: 3, b: 5}
   * @symb R.pluck('x', [{x: 1, y: 2}, {x: 3, y: 4}, {x: 5, y: 6}]) = [1, 3, 5]
   * @symb R.pluck(0, [[1, 2], [3, 4], [5, 6]]) = [1, 3, 5]
   */
  var pluck = _curry2(function pluck(p, list) {
    return map(prop(p), list);
  });

  /**
   * Returns a single item by iterating through the list, successively calling
   * the iterator function and passing it an accumulator value and the current
   * value from the array, and then passing the result to the next call.
   *
   * The iterator function receives two values: *(acc, value)*. It may use
   * [`R.reduced`](#reduced) to shortcut the iteration.
   *
   * The arguments' order of [`reduceRight`](#reduceRight)'s iterator function
   * is *(value, acc)*.
   *
   * Note: `R.reduce` does not skip deleted or unassigned indices (sparse
   * arrays), unlike the native `Array.prototype.reduce` method. For more details
   * on this behavior, see:
   * https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/reduce#Description
   *
   * Dispatches to the `reduce` method of the third argument, if present. When
   * doing so, it is up to the user to handle the [`R.reduced`](#reduced)
   * shortcuting, as this is not implemented by `reduce`.
   *
   * @func
   * @memberOf R
   * @since v0.1.0
   * @category List
   * @sig ((a, b) -> a) -> a -> [b] -> a
   * @param {Function} fn The iterator function. Receives two values, the accumulator and the
   *        current element from the array.
   * @param {*} acc The accumulator value.
   * @param {Array} list The list to iterate over.
   * @return {*} The final, accumulated value.
   * @see R.reduced, R.addIndex, R.reduceRight
   * @example
   *
   *      R.reduce(R.subtract, 0, [1, 2, 3, 4]) // => ((((0 - 1) - 2) - 3) - 4) = -10
   *      //          -               -10
   *      //         / \              / \
   *      //        -   4           -6   4
   *      //       / \              / \
   *      //      -   3   ==>     -3   3
   *      //     / \              / \
   *      //    -   2           -1   2
   *      //   / \              / \
   *      //  0   1            0   1
   *
   * @symb R.reduce(f, a, [b, c, d]) = f(f(f(a, b), c), d)
   */
  var reduce = _curry3(_reduce);

  /**
   * Takes a list of predicates and returns a predicate that returns true for a
   * given list of arguments if every one of the provided predicates is satisfied
   * by those arguments.
   *
   * The function returned is a curried function whose arity matches that of the
   * highest-arity predicate.
   *
   * @func
   * @memberOf R
   * @since v0.9.0
   * @category Logic
   * @sig [(*... -> Boolean)] -> (*... -> Boolean)
   * @param {Array} predicates An array of predicates to check
   * @return {Function} The combined predicate
   * @see R.anyPass
   * @example
   *
   *      const isQueen = R.propEq('rank', 'Q');
   *      const isSpade = R.propEq('suit', '♠︎');
   *      const isQueenOfSpades = R.allPass([isQueen, isSpade]);
   *
   *      isQueenOfSpades({rank: 'Q', suit: '♣︎'}); //=> false
   *      isQueenOfSpades({rank: 'Q', suit: '♠︎'}); //=> true
   */
  var allPass = _curry1(function allPass(preds) {
    return curryN(reduce(max, 0, pluck('length', preds)), function() {
      var idx = 0;
      var len = preds.length;
      while (idx < len) {
        if (!preds[idx].apply(this, arguments)) {
          return false;
        }
        idx += 1;
      }
      return true;
    });
  });

  /**
   * Returns a function that always returns the given value. Note that for
   * non-primitives the value returned is a reference to the original value.
   *
   * This function is known as `const`, `constant`, or `K` (for K combinator) in
   * other languages and libraries.
   *
   * @func
   * @memberOf R
   * @since v0.1.0
   * @category Function
   * @sig a -> (* -> a)
   * @param {*} val The value to wrap in a function
   * @return {Function} A Function :: * -> val.
   * @example
   *
   *      const t = R.always('Tee');
   *      t(); //=> 'Tee'
   */
  var always = _curry1(function always(val) {
    return function() {
      return val;
    };
  });

  /**
   * Returns `true` if both arguments are `true`; `false` otherwise.
   *
   * @func
   * @memberOf R
   * @since v0.1.0
   * @category Logic
   * @sig a -> b -> a | b
   * @param {Any} a
   * @param {Any} b
   * @return {Any} the first argument if it is falsy, otherwise the second argument.
   * @see R.both, R.xor
   * @example
   *
   *      R.and(true, true); //=> true
   *      R.and(true, false); //=> false
   *      R.and(false, true); //=> false
   *      R.and(false, false); //=> false
   */
  var and = _curry2(function and(a, b) {
    return a && b;
  });

  function XAny(f, xf) {
    this.xf = xf;
    this.f = f;
    this.any = false;
  }
  XAny.prototype['@@transducer/init'] = _xfBase.init;
  XAny.prototype['@@transducer/result'] = function(result) {
    if (!this.any) {
      result = this.xf['@@transducer/step'](result, false);
    }
    return this.xf['@@transducer/result'](result);
  };
  XAny.prototype['@@transducer/step'] = function(result, input) {
    if (this.f(input)) {
      this.any = true;
      result = _reduced(this.xf['@@transducer/step'](result, true));
    }
    return result;
  };

  var _xany = _curry2(function _xany(f, xf) { return new XAny(f, xf); });

  /**
   * Returns `true` if at least one of the elements of the list match the predicate,
   * `false` otherwise.
   *
   * Dispatches to the `any` method of the second argument, if present.
   *
   * Acts as a transducer if a transformer is given in list position.
   *
   * @func
   * @memberOf R
   * @since v0.1.0
   * @category List
   * @sig (a -> Boolean) -> [a] -> Boolean
   * @param {Function} fn The predicate function.
   * @param {Array} list The array to consider.
   * @return {Boolean} `true` if the predicate is satisfied by at least one element, `false`
   *         otherwise.
   * @see R.all, R.none, R.transduce
   * @example
   *
   *      const lessThan0 = R.flip(R.lt)(0);
   *      const lessThan2 = R.flip(R.lt)(2);
   *      R.any(lessThan0)([1, 2]); //=> false
   *      R.any(lessThan2)([1, 2]); //=> true
   */
  var any = _curry2(_dispatchable(['any'], _xany, function any(fn, list) {
    var idx = 0;
    while (idx < list.length) {
      if (fn(list[idx])) {
        return true;
      }
      idx += 1;
    }
    return false;
  }));

  /**
   * Takes a list of predicates and returns a predicate that returns true for a
   * given list of arguments if at least one of the provided predicates is
   * satisfied by those arguments.
   *
   * The function returned is a curried function whose arity matches that of the
   * highest-arity predicate.
   *
   * @func
   * @memberOf R
   * @since v0.9.0
   * @category Logic
   * @sig [(*... -> Boolean)] -> (*... -> Boolean)
   * @param {Array} predicates An array of predicates to check
   * @return {Function} The combined predicate
   * @see R.allPass
   * @example
   *
   *      const isClub = R.propEq('suit', '♣');
   *      const isSpade = R.propEq('suit', '♠');
   *      const isBlackCard = R.anyPass([isClub, isSpade]);
   *
   *      isBlackCard({rank: '10', suit: '♣'}); //=> true
   *      isBlackCard({rank: 'Q', suit: '♠'}); //=> true
   *      isBlackCard({rank: 'Q', suit: '♦'}); //=> false
   */
  var anyPass = _curry1(function anyPass(preds) {
    return curryN(reduce(max, 0, pluck('length', preds)), function() {
      var idx = 0;
      var len = preds.length;
      while (idx < len) {
        if (preds[idx].apply(this, arguments)) {
          return true;
        }
        idx += 1;
      }
      return false;
    });
  });

  /**
   * ap applies a list of functions to a list of values.
   *
   * Dispatches to the `ap` method of the second argument, if present. Also
   * treats curried functions as applicatives.
   *
   * @func
   * @memberOf R
   * @since v0.3.0
   * @category Function
   * @sig [a -> b] -> [a] -> [b]
   * @sig Apply f => f (a -> b) -> f a -> f b
   * @sig (r -> a -> b) -> (r -> a) -> (r -> b)
   * @param {*} applyF
   * @param {*} applyX
   * @return {*}
   * @example
   *
   *      R.ap([R.multiply(2), R.add(3)], [1,2,3]); //=> [2, 4, 6, 4, 5, 6]
   *      R.ap([R.concat('tasty '), R.toUpper], ['pizza', 'salad']); //=> ["tasty pizza", "tasty salad", "PIZZA", "SALAD"]
   *
   *      // R.ap can also be used as S combinator
   *      // when only two functions are passed
   *      R.ap(R.concat, R.toUpper)('Ramda') //=> 'RamdaRAMDA'
   * @symb R.ap([f, g], [a, b]) = [f(a), f(b), g(a), g(b)]
   */
  var ap = _curry2(function ap(applyF, applyX) {
    return (
      typeof applyX['fantasy-land/ap'] === 'function'
        ? applyX['fantasy-land/ap'](applyF)
        : typeof applyF.ap === 'function'
          ? applyF.ap(applyX)
          : typeof applyF === 'function'
            ? function(x) { return applyF(x)(applyX(x)); }
            : _reduce(function(acc, f) { return _concat(acc, map(f, applyX)); }, [], applyF)
    );
  });

  function _aperture(n, list) {
    var idx = 0;
    var limit = list.length - (n - 1);
    var acc = new Array(limit >= 0 ? limit : 0);
    while (idx < limit) {
      acc[idx] = Array.prototype.slice.call(list, idx, idx + n);
      idx += 1;
    }
    return acc;
  }

  function XAperture(n, xf) {
    this.xf = xf;
    this.pos = 0;
    this.full = false;
    this.acc = new Array(n);
  }
  XAperture.prototype['@@transducer/init'] = _xfBase.init;
  XAperture.prototype['@@transducer/result'] = function(result) {
    this.acc = null;
    return this.xf['@@transducer/result'](result);
  };
  XAperture.prototype['@@transducer/step'] = function(result, input) {
    this.store(input);
    return this.full ? this.xf['@@transducer/step'](result, this.getCopy()) : result;
  };
  XAperture.prototype.store = function(input) {
    this.acc[this.pos] = input;
    this.pos += 1;
    if (this.pos === this.acc.length) {
      this.pos = 0;
      this.full = true;
    }
  };
  XAperture.prototype.getCopy = function() {
    return _concat(Array.prototype.slice.call(this.acc, this.pos),
      Array.prototype.slice.call(this.acc, 0, this.pos)
    );
  };

  var _xaperture = _curry2(function _xaperture(n, xf) { return new XAperture(n, xf); });

  /**
   * Returns a new list, composed of n-tuples of consecutive elements. If `n` is
   * greater than the length of the list, an empty list is returned.
   *
   * Acts as a transducer if a transformer is given in list position.
   *
   * @func
   * @memberOf R
   * @since v0.12.0
   * @category List
   * @sig Number -> [a] -> [[a]]
   * @param {Number} n The size of the tuples to create
   * @param {Array} list The list to split into `n`-length tuples
   * @return {Array} The resulting list of `n`-length tuples
   * @see R.transduce
   * @example
   *
   *      R.aperture(2, [1, 2, 3, 4, 5]); //=> [[1, 2], [2, 3], [3, 4], [4, 5]]
   *      R.aperture(3, [1, 2, 3, 4, 5]); //=> [[1, 2, 3], [2, 3, 4], [3, 4, 5]]
   *      R.aperture(7, [1, 2, 3, 4, 5]); //=> []
   */
  var aperture = _curry2(_dispatchable([], _xaperture, _aperture));

  /**
   * Returns a new list containing the contents of the given list, followed by
   * the given element.
   *
   * @func
   * @memberOf R
   * @since v0.1.0
   * @category List
   * @sig a -> [a] -> [a]
   * @param {*} el The element to add to the end of the new list.
   * @param {Array} list The list of elements to add a new item to.
   *        list.
   * @return {Array} A new list containing the elements of the old list followed by `el`.
   * @see R.prepend
   * @example
   *
   *      R.append('tests', ['write', 'more']); //=> ['write', 'more', 'tests']
   *      R.append('tests', []); //=> ['tests']
   *      R.append(['tests'], ['write', 'more']); //=> ['write', 'more', ['tests']]
   */
  var append = _curry2(function append(el, list) {
    return _concat(list, [el]);
  });

  /**
   * Applies function `fn` to the argument list `args`. This is useful for
   * creating a fixed-arity function from a variadic function. `fn` should be a
   * bound function if context is significant.
   *
   * @func
   * @memberOf R
   * @since v0.7.0
   * @category Function
   * @sig (*... -> a) -> [*] -> a
   * @param {Function} fn The function which will be called with `args`
   * @param {Array} args The arguments to call `fn` with
   * @return {*} result The result, equivalent to `fn(...args)`
   * @see R.call, R.unapply
   * @example
   *
   *      const nums = [1, 2, 3, -99, 42, 6, 7];
   *      R.apply(Math.max, nums); //=> 42
   * @symb R.apply(f, [a, b, c]) = f(a, b, c)
   */
  var apply = _curry2(function apply(fn, args) {
    return fn.apply(this, args);
  });

  /**
   * Returns a list of all the enumerable own properties of the supplied object.
   * Note that the order of the output array is not guaranteed across different
   * JS platforms.
   *
   * @func
   * @memberOf R
   * @since v0.1.0
   * @category Object
   * @sig {k: v} -> [v]
   * @param {Object} obj The object to extract values from
   * @return {Array} An array of the values of the object's own properties.
   * @see R.valuesIn, R.keys
   * @example
   *
   *      R.values({a: 1, b: 2, c: 3}); //=> [1, 2, 3]
   */
  var values = _curry1(function values(obj) {
    var props = keys(obj);
    var len = props.length;
    var vals = [];
    var idx = 0;
    while (idx < len) {
      vals[idx] = obj[props[idx]];
      idx += 1;
    }
    return vals;
  });

  // Use custom mapValues function to avoid issues with specs that include a "map" key and R.map
  // delegating calls to .map
  function mapValues(fn, obj) {
    return keys(obj).reduce(function(acc, key) {
      acc[key] = fn(obj[key]);
      return acc;
    }, {});
  }

  /**
   * Given a spec object recursively mapping properties to functions, creates a
   * function producing an object of the same structure, by mapping each property
   * to the result of calling its associated function with the supplied arguments.
   *
   * @func
   * @memberOf R
   * @since v0.20.0
   * @category Function
   * @sig {k: ((a, b, ..., m) -> v)} -> ((a, b, ..., m) -> {k: v})
   * @param {Object} spec an object recursively mapping properties to functions for
   *        producing the values for these properties.
   * @return {Function} A function that returns an object of the same structure
   * as `spec', with each property set to the value returned by calling its
   * associated function with the supplied arguments.
   * @see R.converge, R.juxt
   * @example
   *
   *      const getMetrics = R.applySpec({
   *        sum: R.add,
   *        nested: { mul: R.multiply }
   *      });
   *      getMetrics(2, 4); // => { sum: 6, nested: { mul: 8 } }
   * @symb R.applySpec({ x: f, y: { z: g } })(a, b) = { x: f(a, b), y: { z: g(a, b) } }
   */
  var applySpec = _curry1(function applySpec(spec) {
    spec = mapValues(
      function(v) { return typeof v == 'function' ? v : applySpec(v); },
      spec
    );

    return curryN(
      reduce(max, 0, pluck('length', values(spec))),
      function() {
        var args = arguments;
        return mapValues(function(f) { return apply(f, args); }, spec);
      });
  });

  /**
   * Takes a value and applies a function to it.
   *
   * This function is also known as the `thrush` combinator.
   *
   * @func
   * @memberOf R
   * @since v0.25.0
   * @category Function
   * @sig a -> (a -> b) -> b
   * @param {*} x The value
   * @param {Function} f The function to apply
   * @return {*} The result of applying `f` to `x`
   * @example
   *
   *      const t42 = R.applyTo(42);
   *      t42(R.identity); //=> 42
   *      t42(R.add(1)); //=> 43
   */
  var applyTo = _curry2(function applyTo(x, f) { return f(x); });

  /**
   * Makes an ascending comparator function out of a function that returns a value
   * that can be compared with `<` and `>`.
   *
   * @func
   * @memberOf R
   * @since v0.23.0
   * @category Function
   * @sig Ord b => (a -> b) -> a -> a -> Number
   * @param {Function} fn A function of arity one that returns a value that can be compared
   * @param {*} a The first item to be compared.
   * @param {*} b The second item to be compared.
   * @return {Number} `-1` if fn(a) < fn(b), `1` if fn(b) < fn(a), otherwise `0`
   * @see R.descend
   * @example
   *
   *      const byAge = R.ascend(R.prop('age'));
   *      const people = [
   *        { name: 'Emma', age: 70 },
   *        { name: 'Peter', age: 78 },
   *        { name: 'Mikhail', age: 62 },
   *      ];
   *      const peopleByYoungestFirst = R.sort(byAge, people);
   *        //=> [{ name: 'Mikhail', age: 62 },{ name: 'Emma', age: 70 }, { name: 'Peter', age: 78 }]
   */
  var ascend = _curry3(function ascend(fn, a, b) {
    var aa = fn(a);
    var bb = fn(b);
    return aa < bb ? -1 : aa > bb ? 1 : 0;
  });

  /**
   * Makes a shallow clone of an object, setting or overriding the specified
   * property with the given value. Note that this copies and flattens prototype
   * properties onto the new object as well. All non-primitive properties are
   * copied by reference.
   *
   * @func
   * @memberOf R
   * @since v0.8.0
   * @category Object
   * @sig String -> a -> {k: v} -> {k: v}
   * @param {String} prop The property name to set
   * @param {*} val The new value
   * @param {Object} obj The object to clone
   * @return {Object} A new object equivalent to the original except for the changed property.
   * @see R.dissoc, R.pick
   * @example
   *
   *      R.assoc('c', 3, {a: 1, b: 2}); //=> {a: 1, b: 2, c: 3}
   */
  var assoc = _curry3(function assoc(prop, val, obj) {
    var result = {};
    for (var p in obj) {
      result[p] = obj[p];
    }
    result[prop] = val;
    return result;
  });

  /**
   * Checks if the input value is `null` or `undefined`.
   *
   * @func
   * @memberOf R
   * @since v0.9.0
   * @category Type
   * @sig * -> Boolean
   * @param {*} x The value to test.
   * @return {Boolean} `true` if `x` is `undefined` or `null`, otherwise `false`.
   * @example
   *
   *      R.isNil(null); //=> true
   *      R.isNil(undefined); //=> true
   *      R.isNil(0); //=> false
   *      R.isNil([]); //=> false
   */
  var isNil = _curry1(function isNil(x) { return x == null; });

  /**
   * Makes a shallow clone of an object, setting or overriding the nodes required
   * to create the given path, and placing the specific value at the tail end of
   * that path. Note that this copies and flattens prototype properties onto the
   * new object as well. All non-primitive properties are copied by reference.
   *
   * @func
   * @memberOf R
   * @since v0.8.0
   * @category Object
   * @typedefn Idx = String | Int
   * @sig [Idx] -> a -> {a} -> {a}
   * @param {Array} path the path to set
   * @param {*} val The new value
   * @param {Object} obj The object to clone
   * @return {Object} A new object equivalent to the original except along the specified path.
   * @see R.dissocPath
   * @example
   *
   *      R.assocPath(['a', 'b', 'c'], 42, {a: {b: {c: 0}}}); //=> {a: {b: {c: 42}}}
   *
   *      // Any missing or non-object keys in path will be overridden
   *      R.assocPath(['a', 'b', 'c'], 42, {a: 5}); //=> {a: {b: {c: 42}}}
   */
  var assocPath = _curry3(function assocPath(path, val, obj) {
    if (path.length === 0) {
      return val;
    }
    var idx = path[0];
    if (path.length > 1) {
      var nextObj = (!isNil(obj) && _has(idx, obj)) ? obj[idx] : _isInteger(path[1]) ? [] : {};
      val = assocPath(Array.prototype.slice.call(path, 1), val, nextObj);
    }
    if (_isInteger(idx) && _isArray(obj)) {
      var arr = [].concat(obj);
      arr[idx] = val;
      return arr;
    } else {
      return assoc(idx, val, obj);
    }
  });

  /**
   * Wraps a function of any arity (including nullary) in a function that accepts
   * exactly `n` parameters. Any extraneous parameters will not be passed to the
   * supplied function.
   *
   * @func
   * @memberOf R
   * @since v0.1.0
   * @category Function
   * @sig Number -> (* -> a) -> (* -> a)
   * @param {Number} n The desired arity of the new function.
   * @param {Function} fn The function to wrap.
   * @return {Function} A new function wrapping `fn`. The new function is guaranteed to be of
   *         arity `n`.
   * @see R.binary, R.unary
   * @example
   *
   *      const takesTwoArgs = (a, b) => [a, b];
   *
   *      takesTwoArgs.length; //=> 2
   *      takesTwoArgs(1, 2); //=> [1, 2]
   *
   *      const takesOneArg = R.nAry(1, takesTwoArgs);
   *      takesOneArg.length; //=> 1
   *      // Only `n` arguments are passed to the wrapped function
   *      takesOneArg(1, 2); //=> [1, undefined]
   * @symb R.nAry(0, f)(a, b) = f()
   * @symb R.nAry(1, f)(a, b) = f(a)
   * @symb R.nAry(2, f)(a, b) = f(a, b)
   */
  var nAry = _curry2(function nAry(n, fn) {
    switch (n) {
      case 0: return function() {return fn.call(this);};
      case 1: return function(a0) {return fn.call(this, a0);};
      case 2: return function(a0, a1) {return fn.call(this, a0, a1);};
      case 3: return function(a0, a1, a2) {return fn.call(this, a0, a1, a2);};
      case 4: return function(a0, a1, a2, a3) {return fn.call(this, a0, a1, a2, a3);};
      case 5: return function(a0, a1, a2, a3, a4) {return fn.call(this, a0, a1, a2, a3, a4);};
      case 6: return function(a0, a1, a2, a3, a4, a5) {return fn.call(this, a0, a1, a2, a3, a4, a5);};
      case 7: return function(a0, a1, a2, a3, a4, a5, a6) {return fn.call(this, a0, a1, a2, a3, a4, a5, a6);};
      case 8: return function(a0, a1, a2, a3, a4, a5, a6, a7) {return fn.call(this, a0, a1, a2, a3, a4, a5, a6, a7);};
      case 9: return function(a0, a1, a2, a3, a4, a5, a6, a7, a8) {return fn.call(this, a0, a1, a2, a3, a4, a5, a6, a7, a8);};
      case 10: return function(a0, a1, a2, a3, a4, a5, a6, a7, a8, a9) {return fn.call(this, a0, a1, a2, a3, a4, a5, a6, a7, a8, a9);};
      default: throw new Error('First argument to nAry must be a non-negative integer no greater than ten');
    }
  });

  /**
   * Wraps a function of any arity (including nullary) in a function that accepts
   * exactly 2 parameters. Any extraneous parameters will not be passed to the
   * supplied function.
   *
   * @func
   * @memberOf R
   * @since v0.2.0
   * @category Function
   * @sig (* -> c) -> (a, b -> c)
   * @param {Function} fn The function to wrap.
   * @return {Function} A new function wrapping `fn`. The new function is guaranteed to be of
   *         arity 2.
   * @see R.nAry, R.unary
   * @example
   *
   *      const takesThreeArgs = function(a, b, c) {
   *        return [a, b, c];
   *      };
   *      takesThreeArgs.length; //=> 3
   *      takesThreeArgs(1, 2, 3); //=> [1, 2, 3]
   *
   *      const takesTwoArgs = R.binary(takesThreeArgs);
   *      takesTwoArgs.length; //=> 2
   *      // Only 2 arguments are passed to the wrapped function
   *      takesTwoArgs(1, 2, 3); //=> [1, 2, undefined]
   * @symb R.binary(f)(a, b, c) = f(a, b)
   */
  var binary = _curry1(function binary(fn) {
    return nAry(2, fn);
  });

  function _isFunction(x) {
    var type = Object.prototype.toString.call(x);
    return type  === '[object Function]' ||
      type === '[object AsyncFunction]' ||
      type === '[object GeneratorFunction]' ||
      type === '[object AsyncGeneratorFunction]';
  }

  /**
   * "lifts" a function to be the specified arity, so that it may "map over" that
   * many lists, Functions or other objects that satisfy the [FantasyLand Apply spec](https://github.com/fantasyland/fantasy-land#apply).
   *
   * @func
   * @memberOf R
   * @since v0.7.0
   * @category Function
   * @sig Number -> (*... -> *) -> ([*]... -> [*])
   * @param {Function} fn The function to lift into higher context
   * @return {Function} The lifted function.
   * @see R.lift, R.ap
   * @example
   *
   *      const madd3 = R.liftN(3, (...args) => R.sum(args));
   *      madd3([1,2,3], [1,2,3], [1]); //=> [3, 4, 5, 4, 5, 6, 5, 6, 7]
   */
  var liftN = _curry2(function liftN(arity, fn) {
    var lifted = curryN(arity, fn);
    return curryN(arity, function() {
      return _reduce(ap, map(lifted, arguments[0]), Array.prototype.slice.call(arguments, 1));
    });
  });

  /**
   * "lifts" a function of arity > 1 so that it may "map over" a list, Function or other
   * object that satisfies the [FantasyLand Apply spec](https://github.com/fantasyland/fantasy-land#apply).
   *
   * @func
   * @memberOf R
   * @since v0.7.0
   * @category Function
   * @sig (*... -> *) -> ([*]... -> [*])
   * @param {Function} fn The function to lift into higher context
   * @return {Function} The lifted function.
   * @see R.liftN
   * @example
   *
   *      const madd3 = R.lift((a, b, c) => a + b + c);
   *
   *      madd3([1,2,3], [1,2,3], [1]); //=> [3, 4, 5, 4, 5, 6, 5, 6, 7]
   *
   *      const madd5 = R.lift((a, b, c, d, e) => a + b + c + d + e);
   *
   *      madd5([1,2], [3], [4, 5], [6], [7, 8]); //=> [21, 22, 22, 23, 22, 23, 23, 24]
   */
  var lift = _curry1(function lift(fn) {
    return liftN(fn.length, fn);
  });

  /**
   * A function which calls the two provided functions and returns the `&&`
   * of the results.
   * It returns the result of the first function if it is false-y and the result
   * of the second function otherwise. Note that this is short-circuited,
   * meaning that the second function will not be invoked if the first returns a
   * false-y value.
   *
   * In addition to functions, `R.both` also accepts any fantasy-land compatible
   * applicative functor.
   *
   * @func
   * @memberOf R
   * @since v0.12.0
   * @category Logic
   * @sig (*... -> Boolean) -> (*... -> Boolean) -> (*... -> Boolean)
   * @param {Function} f A predicate
   * @param {Function} g Another predicate
   * @return {Function} a function that applies its arguments to `f` and `g` and `&&`s their outputs together.
   * @see R.and
   * @example
   *
   *      const gt10 = R.gt(R.__, 10)
   *      const lt20 = R.lt(R.__, 20)
   *      const f = R.both(gt10, lt20);
   *      f(15); //=> true
   *      f(30); //=> false
   *
   *      R.both(Maybe.Just(false), Maybe.Just(55)); // => Maybe.Just(false)
   *      R.both([false, false, 'a'], [11]); //=> [false, false, 11]
   */
  var both = _curry2(function both(f, g) {
    return _isFunction(f) ?
      function _both() {
        return f.apply(this, arguments) && g.apply(this, arguments);
      } :
      lift(and)(f, g);
  });

  /**
   * Returns a curried equivalent of the provided function. The curried function
   * has two unusual capabilities. First, its arguments needn't be provided one
   * at a time. If `f` is a ternary function and `g` is `R.curry(f)`, the
   * following are equivalent:
   *
   *   - `g(1)(2)(3)`
   *   - `g(1)(2, 3)`
   *   - `g(1, 2)(3)`
   *   - `g(1, 2, 3)`
   *
   * Secondly, the special placeholder value [`R.__`](#__) may be used to specify
   * "gaps", allowing partial application of any combination of arguments,
   * regardless of their positions. If `g` is as above and `_` is [`R.__`](#__),
   * the following are equivalent:
   *
   *   - `g(1, 2, 3)`
   *   - `g(_, 2, 3)(1)`
   *   - `g(_, _, 3)(1)(2)`
   *   - `g(_, _, 3)(1, 2)`
   *   - `g(_, 2)(1)(3)`
   *   - `g(_, 2)(1, 3)`
   *   - `g(_, 2)(_, 3)(1)`
   *
   * @func
   * @memberOf R
   * @since v0.1.0
   * @category Function
   * @sig (* -> a) -> (* -> a)
   * @param {Function} fn The function to curry.
   * @return {Function} A new, curried function.
   * @see R.curryN, R.partial
   * @example
   *
   *      const addFourNumbers = (a, b, c, d) => a + b + c + d;
   *
   *      const curriedAddFourNumbers = R.curry(addFourNumbers);
   *      const f = curriedAddFourNumbers(1, 2);
   *      const g = f(3);
   *      g(4); //=> 10
   */
  var curry = _curry1(function curry(fn) {
    return curryN(fn.length, fn);
  });

  /**
   * Returns the result of calling its first argument with the remaining
   * arguments. This is occasionally useful as a converging function for
   * [`R.converge`](#converge): the first branch can produce a function while the
   * remaining branches produce values to be passed to that function as its
   * arguments.
   *
   * @func
   * @memberOf R
   * @since v0.9.0
   * @category Function
   * @sig (*... -> a),*... -> a
   * @param {Function} fn The function to apply to the remaining arguments.
   * @param {...*} args Any number of positional arguments.
   * @return {*}
   * @see R.apply
   * @example
   *
   *      R.call(R.add, 1, 2); //=> 3
   *
   *      const indentN = R.pipe(R.repeat(' '),
   *                           R.join(''),
   *                           R.replace(/^(?!$)/gm));
   *
   *      const format = R.converge(R.call, [
   *                                  R.pipe(R.prop('indent'), indentN),
   *                                  R.prop('value')
   *                              ]);
   *
   *      format({indent: 2, value: 'foo\nbar\nbaz\n'}); //=> '  foo\n  bar\n  baz\n'
   * @symb R.call(f, a, b) = f(a, b)
   */
  var call = curry(function call(fn) {
    return fn.apply(this, Array.prototype.slice.call(arguments, 1));
  });

  /**
   * `_makeFlat` is a helper function that returns a one-level or fully recursive
   * function based on the flag passed in.
   *
   * @private
   */
  function _makeFlat(recursive) {
    return function flatt(list) {
      var value, jlen, j;
      var result = [];
      var idx = 0;
      var ilen = list.length;

      while (idx < ilen) {
        if (_isArrayLike(list[idx])) {
          value = recursive ? flatt(list[idx]) : list[idx];
          j = 0;
          jlen = value.length;
          while (j < jlen) {
            result[result.length] = value[j];
            j += 1;
          }
        } else {
          result[result.length] = list[idx];
        }
        idx += 1;
      }
      return result;
    };
  }

  function _forceReduced(x) {
    return {
      '@@transducer/value': x,
      '@@transducer/reduced': true
    };
  }

  var preservingReduced = function(xf) {
    return {
      '@@transducer/init': _xfBase.init,
      '@@transducer/result': function(result) {
        return xf['@@transducer/result'](result);
      },
      '@@transducer/step': function(result, input) {
        var ret = xf['@@transducer/step'](result, input);
        return ret['@@transducer/reduced'] ? _forceReduced(ret) : ret;
      }
    };
  };

  var _flatCat = function _xcat(xf) {
    var rxf = preservingReduced(xf);
    return {
      '@@transducer/init': _xfBase.init,
      '@@transducer/result': function(result) {
        return rxf['@@transducer/result'](result);
      },
      '@@transducer/step': function(result, input) {
        return !_isArrayLike(input) ? _reduce(rxf, result, [input]) : _reduce(rxf, result, input);
      }
    };
  };

  var _xchain = _curry2(function _xchain(f, xf) {
    return map(f, _flatCat(xf));
  });

  /**
   * `chain` maps a function over a list and concatenates the results. `chain`
   * is also known as `flatMap` in some libraries.
   *
   * Dispatches to the `chain` method of the second argument, if present,
   * according to the [FantasyLand Chain spec](https://github.com/fantasyland/fantasy-land#chain).
   *
   * If second argument is a function, `chain(f, g)(x)` is equivalent to `f(g(x), x)`.
   *
   * Acts as a transducer if a transformer is given in list position.
   *
   * @func
   * @memberOf R
   * @since v0.3.0
   * @category List
   * @sig Chain m => (a -> m b) -> m a -> m b
   * @param {Function} fn The function to map with
   * @param {Array} list The list to map over
   * @return {Array} The result of flat-mapping `list` with `fn`
   * @example
   *
   *      const duplicate = n => [n, n];
   *      R.chain(duplicate, [1, 2, 3]); //=> [1, 1, 2, 2, 3, 3]
   *
   *      R.chain(R.append, R.head)([1, 2, 3]); //=> [1, 2, 3, 1]
   */
  var chain = _curry2(_dispatchable(['fantasy-land/chain', 'chain'], _xchain, function chain(fn, monad) {
    if (typeof monad === 'function') {
      return function(x) { return fn(monad(x))(x); };
    }
    return _makeFlat(false)(map(fn, monad));
  }));

  /**
   * Restricts a number to be within a range.
   *
   * Also works for other ordered types such as Strings and Dates.
   *
   * @func
   * @memberOf R
   * @since v0.20.0
   * @category Relation
   * @sig Ord a => a -> a -> a -> a
   * @param {Number} minimum The lower limit of the clamp (inclusive)
   * @param {Number} maximum The upper limit of the clamp (inclusive)
   * @param {Number} value Value to be clamped
   * @return {Number} Returns `minimum` when `val < minimum`, `maximum` when `val > maximum`, returns `val` otherwise
   * @example
   *
   *      R.clamp(1, 10, -5) // => 1
   *      R.clamp(1, 10, 15) // => 10
   *      R.clamp(1, 10, 4)  // => 4
   */
  var clamp = _curry3(function clamp(min, max, value) {
    if (min > max) {
      throw new Error('min must not be greater than max in clamp(min, max, value)');
    }
    return value < min
      ? min
      : value > max
        ? max
        : value;
  });

  function _cloneRegExp(pattern) {
    return new RegExp(pattern.source, (pattern.global     ? 'g' : '') +
                                      (pattern.ignoreCase ? 'i' : '') +
                                      (pattern.multiline  ? 'm' : '') +
                                      (pattern.sticky     ? 'y' : '') +
                                      (pattern.unicode    ? 'u' : ''));
  }

  /**
   * Gives a single-word string description of the (native) type of a value,
   * returning such answers as 'Object', 'Number', 'Array', or 'Null'. Does not
   * attempt to distinguish user Object types any further, reporting them all as
   * 'Object'.
   *
   * @func
   * @memberOf R
   * @since v0.8.0
   * @category Type
   * @sig (* -> {*}) -> String
   * @param {*} val The value to test
   * @return {String}
   * @example
   *
   *      R.type({}); //=> "Object"
   *      R.type(1); //=> "Number"
   *      R.type(false); //=> "Boolean"
   *      R.type('s'); //=> "String"
   *      R.type(null); //=> "Null"
   *      R.type([]); //=> "Array"
   *      R.type(/[A-z]/); //=> "RegExp"
   *      R.type(() => {}); //=> "Function"
   *      R.type(undefined); //=> "Undefined"
   */
  var type = _curry1(function type(val) {
    return val === null
      ? 'Null'
      : val === undefined
        ? 'Undefined'
        : Object.prototype.toString.call(val).slice(8, -1);
  });

  /**
   * Copies an object.
   *
   * @private
   * @param {*} value The value to be copied
   * @param {Array} refFrom Array containing the source references
   * @param {Array} refTo Array containing the copied source references
   * @param {Boolean} deep Whether or not to perform deep cloning.
   * @return {*} The copied value.
   */
  function _clone(value, refFrom, refTo, deep) {
    var copy = function copy(copiedValue) {
      var len = refFrom.length;
      var idx = 0;
      while (idx < len) {
        if (value === refFrom[idx]) {
          return refTo[idx];
        }
        idx += 1;
      }
      refFrom[idx + 1] = value;
      refTo[idx + 1] = copiedValue;
      for (var key in value) {
        copiedValue[key] = deep ?
          _clone(value[key], refFrom, refTo, true) : value[key];
      }
      return copiedValue;
    };
    switch (type(value)) {
      case 'Object':  return copy({});
      case 'Array':   return copy([]);
      case 'Date':    return new Date(value.valueOf());
      case 'RegExp':  return _cloneRegExp(value);
      default:        return value;
    }
  }

  /**
   * Creates a deep copy of the value which may contain (nested) `Array`s and
   * `Object`s, `Number`s, `String`s, `Boolean`s and `Date`s. `Function`s are
   * assigned by reference rather than copied
   *
   * Dispatches to a `clone` method if present.
   *
   * @func
   * @memberOf R
   * @since v0.1.0
   * @category Object
   * @sig {*} -> {*}
   * @param {*} value The object or array to clone
   * @return {*} A deeply cloned copy of `val`
   * @example
   *
   *      const objects = [{}, {}, {}];
   *      const objectsClone = R.clone(objects);
   *      objects === objectsClone; //=> false
   *      objects[0] === objectsClone[0]; //=> false
   */
  var clone = _curry1(function clone(value) {
    return value != null && typeof value.clone === 'function' ?
      value.clone() :
      _clone(value, [], [], true);
  });

  /**
   * Makes a comparator function out of a function that reports whether the first
   * element is less than the second.
   *
   * @func
   * @memberOf R
   * @since v0.1.0
   * @category Function
   * @sig ((a, b) -> Boolean) -> ((a, b) -> Number)
   * @param {Function} pred A predicate function of arity two which will return `true` if the first argument
   * is less than the second, `false` otherwise
   * @return {Function} A Function :: a -> b -> Int that returns `-1` if a < b, `1` if b < a, otherwise `0`
   * @example
   *
   *      const byAge = R.comparator((a, b) => a.age < b.age);
   *      const people = [
   *        { name: 'Emma', age: 70 },
   *        { name: 'Peter', age: 78 },
   *        { name: 'Mikhail', age: 62 },
   *      ];
   *      const peopleByIncreasingAge = R.sort(byAge, people);
   *        //=> [{ name: 'Mikhail', age: 62 },{ name: 'Emma', age: 70 }, { name: 'Peter', age: 78 }]
   */
  var comparator = _curry1(function comparator(pred) {
    return function(a, b) {
      return pred(a, b) ? -1 : pred(b, a) ? 1 : 0;
    };
  });

  /**
   * A function that returns the `!` of its argument. It will return `true` when
   * passed false-y value, and `false` when passed a truth-y one.
   *
   * @func
   * @memberOf R
   * @since v0.1.0
   * @category Logic
   * @sig * -> Boolean
   * @param {*} a any value
   * @return {Boolean} the logical inverse of passed argument.
   * @see R.complement
   * @example
   *
   *      R.not(true); //=> false
   *      R.not(false); //=> true
   *      R.not(0); //=> true
   *      R.not(1); //=> false
   */
  var not = _curry1(function not(a) {
    return !a;
  });

  /**
   * Takes a function `f` and returns a function `g` such that if called with the same arguments
   * when `f` returns a "truthy" value, `g` returns `false` and when `f` returns a "falsy" value `g` returns `true`.
   *
   * `R.complement` may be applied to any functor
   *
   * @func
   * @memberOf R
   * @since v0.12.0
   * @category Logic
   * @sig (*... -> *) -> (*... -> Boolean)
   * @param {Function} f
   * @return {Function}
   * @see R.not
   * @example
   *
   *      const isNotNil = R.complement(R.isNil);
   *      isNil(null); //=> true
   *      isNotNil(null); //=> false
   *      isNil(7); //=> false
   *      isNotNil(7); //=> true
   */
  var complement = lift(not);

  function _pipe(f, g) {
    return function() {
      return g.call(this, f.apply(this, arguments));
    };
  }

  /**
   * This checks whether a function has a [methodname] function. If it isn't an
   * array it will execute that function otherwise it will default to the ramda
   * implementation.
   *
   * @private
   * @param {Function} fn ramda implemtation
   * @param {String} methodname property to check for a custom implementation
   * @return {Object} Whatever the return value of the method is.
   */
  function _checkForMethod(methodname, fn) {
    return function() {
      var length = arguments.length;
      if (length === 0) {
        return fn();
      }
      var obj = arguments[length - 1];
      return (_isArray(obj) || typeof obj[methodname] !== 'function') ?
        fn.apply(this, arguments) :
        obj[methodname].apply(obj, Array.prototype.slice.call(arguments, 0, length - 1));
    };
  }

  /**
   * Returns the elements of the given list or string (or object with a `slice`
   * method) from `fromIndex` (inclusive) to `toIndex` (exclusive).
   *
   * Dispatches to the `slice` method of the third argument, if present.
   *
   * @func
   * @memberOf R
   * @since v0.1.4
   * @category List
   * @sig Number -> Number -> [a] -> [a]
   * @sig Number -> Number -> String -> String
   * @param {Number} fromIndex The start index (inclusive).
   * @param {Number} toIndex The end index (exclusive).
   * @param {*} list
   * @return {*}
   * @example
   *
   *      R.slice(1, 3, ['a', 'b', 'c', 'd']);        //=> ['b', 'c']
   *      R.slice(1, Infinity, ['a', 'b', 'c', 'd']); //=> ['b', 'c', 'd']
   *      R.slice(0, -1, ['a', 'b', 'c', 'd']);       //=> ['a', 'b', 'c']
   *      R.slice(-3, -1, ['a', 'b', 'c', 'd']);      //=> ['b', 'c']
   *      R.slice(0, 3, 'ramda');                     //=> 'ram'
   */
  var slice = _curry3(_checkForMethod('slice', function slice(fromIndex, toIndex, list) {
    return Array.prototype.slice.call(list, fromIndex, toIndex);
  }));

  /**
   * Returns all but the first element of the given list or string (or object
   * with a `tail` method).
   *
   * Dispatches to the `slice` method of the first argument, if present.
   *
   * @func
   * @memberOf R
   * @since v0.1.0
   * @category List
   * @sig [a] -> [a]
   * @sig String -> String
   * @param {*} list
   * @return {*}
   * @see R.head, R.init, R.last
   * @example
   *
   *      R.tail([1, 2, 3]);  //=> [2, 3]
   *      R.tail([1, 2]);     //=> [2]
   *      R.tail([1]);        //=> []
   *      R.tail([]);         //=> []
   *
   *      R.tail('abc');  //=> 'bc'
   *      R.tail('ab');   //=> 'b'
   *      R.tail('a');    //=> ''
   *      R.tail('');     //=> ''
   */
  var tail = _curry1(_checkForMethod('tail', slice(1, Infinity)));

  /**
   * Performs left-to-right function composition. The first argument may have
   * any arity; the remaining arguments must be unary.
   *
   * In some libraries this function is named `sequence`.
   *
   * **Note:** The result of pipe is not automatically curried.
   *
   * @func
   * @memberOf R
   * @since v0.1.0
   * @category Function
   * @sig (((a, b, ..., n) -> o), (o -> p), ..., (x -> y), (y -> z)) -> ((a, b, ..., n) -> z)
   * @param {...Function} functions
   * @return {Function}
   * @see R.compose
   * @example
   *
   *      const f = R.pipe(Math.pow, R.negate, R.inc);
   *
   *      f(3, 4); // -(3^4) + 1
   * @symb R.pipe(f, g, h)(a, b) = h(g(f(a, b)))
   */
  function pipe() {
    if (arguments.length === 0) {
      throw new Error('pipe requires at least one argument');
    }
    return _arity(
      arguments[0].length,
      reduce(_pipe, arguments[0], tail(arguments))
    );
  }

  /**
   * Returns a new list or string with the elements or characters in reverse
   * order.
   *
   * @func
   * @memberOf R
   * @since v0.1.0
   * @category List
   * @sig [a] -> [a]
   * @sig String -> String
   * @param {Array|String} list
   * @return {Array|String}
   * @example
   *
   *      R.reverse([1, 2, 3]);  //=> [3, 2, 1]
   *      R.reverse([1, 2]);     //=> [2, 1]
   *      R.reverse([1]);        //=> [1]
   *      R.reverse([]);         //=> []
   *
   *      R.reverse('abc');      //=> 'cba'
   *      R.reverse('ab');       //=> 'ba'
   *      R.reverse('a');        //=> 'a'
   *      R.reverse('');         //=> ''
   */
  var reverse = _curry1(function reverse(list) {
    return _isString(list)
      ? list.split('').reverse().join('')
      : Array.prototype.slice.call(list, 0).reverse();
  });

  /**
   * Performs right-to-left function composition. The last argument may have
   * any arity; the remaining arguments must be unary.
   *
   * **Note:** The result of compose is not automatically curried.
   *
   * @func
   * @memberOf R
   * @since v0.1.0
   * @category Function
   * @sig ((y -> z), (x -> y), ..., (o -> p), ((a, b, ..., n) -> o)) -> ((a, b, ..., n) -> z)
   * @param {...Function} ...functions The functions to compose
   * @return {Function}
   * @see R.pipe
   * @example
   *
   *      const classyGreeting = (firstName, lastName) => "The name's " + lastName + ", " + firstName + " " + lastName
   *      const yellGreeting = R.compose(R.toUpper, classyGreeting);
   *      yellGreeting('James', 'Bond'); //=> "THE NAME'S BOND, JAMES BOND"
   *
   *      R.compose(Math.abs, R.add(1), R.multiply(2))(-4) //=> 7
   *
   * @symb R.compose(f, g, h)(a, b) = f(g(h(a, b)))
   */
  function compose() {
    if (arguments.length === 0) {
      throw new Error('compose requires at least one argument');
    }
    return pipe.apply(this, reverse(arguments));
  }

  /**
   * Returns the right-to-left Kleisli composition of the provided functions,
   * each of which must return a value of a type supported by [`chain`](#chain).
   *
   * `R.composeK(h, g, f)` is equivalent to `R.compose(R.chain(h), R.chain(g), f)`.
   *
   * @func
   * @memberOf R
   * @since v0.16.0
   * @category Function
   * @sig Chain m => ((y -> m z), (x -> m y), ..., (a -> m b)) -> (a -> m z)
   * @param {...Function} ...functions The functions to compose
   * @return {Function}
   * @see R.pipeK
   * @deprecated since v0.26.0
   * @example
   *
   *       //  get :: String -> Object -> Maybe *
   *       const get = R.curry((propName, obj) => Maybe(obj[propName]))
   *
   *       //  getStateCode :: Maybe String -> Maybe String
   *       const getStateCode = R.composeK(
   *         R.compose(Maybe.of, R.toUpper),
   *         get('state'),
   *         get('address'),
   *         get('user'),
   *       );
   *       getStateCode({"user":{"address":{"state":"ny"}}}); //=> Maybe.Just("NY")
   *       getStateCode({}); //=> Maybe.Nothing()
   * @symb R.composeK(f, g, h)(a) = R.chain(f, R.chain(g, h(a)))
   */
  function composeK() {
    if (arguments.length === 0) {
      throw new Error('composeK requires at least one argument');
    }
    var init = Array.prototype.slice.call(arguments);
    var last = init.pop();
    return compose(compose.apply(this, map(chain, init)), last);
  }

  function _pipeP(f, g) {
    return function() {
      var ctx = this;
      return f.apply(ctx, arguments).then(function(x) {
        return g.call(ctx, x);
      });
    };
  }

  /**
   * Performs left-to-right composition of one or more Promise-returning
   * functions. The first argument may have any arity; the remaining arguments
   * must be unary.
   *
   * @func
   * @memberOf R
   * @since v0.10.0
   * @category Function
   * @sig ((a -> Promise b), (b -> Promise c), ..., (y -> Promise z)) -> (a -> Promise z)
   * @param {...Function} functions
   * @return {Function}
   * @see R.composeP
   * @deprecated since v0.26.0
   * @example
   *
   *      //  followersForUser :: String -> Promise [User]
   *      const followersForUser = R.pipeP(db.getUserById, db.getFollowers);
   */
  function pipeP() {
    if (arguments.length === 0) {
      throw new Error('pipeP requires at least one argument');
    }
    return _arity(
      arguments[0].length,
      reduce(_pipeP, arguments[0], tail(arguments))
    );
  }

  /**
   * Performs right-to-left composition of one or more Promise-returning
   * functions. The last arguments may have any arity; the remaining
   * arguments must be unary.
   *
   * @func
   * @memberOf R
   * @since v0.10.0
   * @category Function
   * @sig ((y -> Promise z), (x -> Promise y), ..., (a -> Promise b)) -> (a -> Promise z)
   * @param {...Function} functions The functions to compose
   * @return {Function}
   * @see R.pipeP
   * @deprecated since v0.26.0
   * @example
   *
   *      const db = {
   *        users: {
   *          JOE: {
   *            name: 'Joe',
   *            followers: ['STEVE', 'SUZY']
   *          }
   *        }
   *      }
   *
   *      // We'll pretend to do a db lookup which returns a promise
   *      const lookupUser = (userId) => Promise.resolve(db.users[userId])
   *      const lookupFollowers = (user) => Promise.resolve(user.followers)
   *      lookupUser('JOE').then(lookupFollowers)
   *
   *      //  followersForUser :: String -> Promise [UserId]
   *      const followersForUser = R.composeP(lookupFollowers, lookupUser);
   *      followersForUser('JOE').then(followers => console.log('Followers:', followers))
   *      // Followers: ["STEVE","SUZY"]
   */
  function composeP() {
    if (arguments.length === 0) {
      throw new Error('composeP requires at least one argument');
    }
    return pipeP.apply(this, reverse(arguments));
  }

  /**
   * Returns the first element of the given list or string. In some libraries
   * this function is named `first`.
   *
   * @func
   * @memberOf R
   * @since v0.1.0
   * @category List
   * @sig [a] -> a | Undefined
   * @sig String -> String
   * @param {Array|String} list
   * @return {*}
   * @see R.tail, R.init, R.last
   * @example
   *
   *      R.head(['fi', 'fo', 'fum']); //=> 'fi'
   *      R.head([]); //=> undefined
   *
   *      R.head('abc'); //=> 'a'
   *      R.head(''); //=> ''
   */
  var head = nth(0);

  function _identity(x) { return x; }

  /**
   * A function that does nothing but return the parameter supplied to it. Good
   * as a default or placeholder function.
   *
   * @func
   * @memberOf R
   * @since v0.1.0
   * @category Function
   * @sig a -> a
   * @param {*} x The value to return.
   * @return {*} The input value, `x`.
   * @example
   *
   *      R.identity(1); //=> 1
   *
   *      const obj = {};
   *      R.identity(obj) === obj; //=> true
   * @symb R.identity(a) = a
   */
  var identity = _curry1(_identity);

  /**
   * Performs left-to-right function composition using transforming function. The first argument may have
   * any arity; the remaining arguments must be unary.
   *
   * **Note:** The result of pipeWith is not automatically curried. Transforming function is not used on the
   * first argument.
   *
   * @func
   * @memberOf R
   * @since v0.26.0
   * @category Function
   * @sig ((* -> *), [((a, b, ..., n) -> o), (o -> p), ..., (x -> y), (y -> z)]) -> ((a, b, ..., n) -> z)
   * @param {...Function} functions
   * @return {Function}
   * @see R.composeWith, R.pipe
   * @example
   *
   *      const pipeWhileNotNil = R.pipeWith((f, res) => R.isNil(res) ? res : f(res));
   *      const f = pipeWhileNotNil([Math.pow, R.negate, R.inc])
   *
   *      f(3, 4); // -(3^4) + 1
   * @symb R.pipeWith(f)([g, h, i])(...args) = f(i, f(h, g(...args)))
   */
  var pipeWith = _curry2(function pipeWith(xf, list) {
    if (list.length <= 0) {
      return identity;
    }

    var headList = head(list);
    var tailList = tail(list);

    return _arity(headList.length, function() {
      return _reduce(
        function(result, f) {
          return xf.call(this, f, result);
        },
        headList.apply(this, arguments),
        tailList
      );
    });
  });

  /**
   * Performs right-to-left function composition using transforming function. The last argument may have
   * any arity; the remaining arguments must be unary.
   *
   * **Note:** The result of compose is not automatically curried. Transforming function is not used on the
   * last argument.
   *
   * @func
   * @memberOf R
   * @since v0.26.0
   * @category Function
   * @sig ((* -> *), [(y -> z), (x -> y), ..., (o -> p), ((a, b, ..., n) -> o)]) -> ((a, b, ..., n) -> z)
   * @param {...Function} ...functions The functions to compose
   * @return {Function}
   * @see R.compose, R.pipeWith
   * @example
   *
   *      const composeWhileNotNil = R.composeWith((f, res) => R.isNil(res) ? res : f(res));
   *
   *      composeWhileNotNil([R.inc, R.prop('age')])({age: 1}) //=> 2
   *      composeWhileNotNil([R.inc, R.prop('age')])({}) //=> undefined
   *
   * @symb R.composeWith(f)([g, h, i])(...args) = f(g, f(h, i(...args)))
   */
  var composeWith = _curry2(function composeWith(xf, list) {
    return pipeWith.apply(this, [xf, reverse(list)]);
  });

  function _arrayFromIterator(iter) {
    var list = [];
    var next;
    while (!(next = iter.next()).done) {
      list.push(next.value);
    }
    return list;
  }

  function _includesWith(pred, x, list) {
    var idx = 0;
    var len = list.length;

    while (idx < len) {
      if (pred(x, list[idx])) {
        return true;
      }
      idx += 1;
    }
    return false;
  }

  function _functionName(f) {
    // String(x => x) evaluates to "x => x", so the pattern may not match.
    var match = String(f).match(/^function (\w*)/);
    return match == null ? '' : match[1];
  }

  // Based on https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/is
  function _objectIs(a, b) {
    // SameValue algorithm
    if (a === b) { // Steps 1-5, 7-10
      // Steps 6.b-6.e: +0 != -0
      return a !== 0 || 1 / a === 1 / b;
    } else {
      // Step 6.a: NaN == NaN
      return a !== a && b !== b;
    }
  }

  var _objectIs$1 = typeof Object.is === 'function' ? Object.is : _objectIs;

  /**
   * private _uniqContentEquals function.
   * That function is checking equality of 2 iterator contents with 2 assumptions
   * - iterators lengths are the same
   * - iterators values are unique
   *
   * false-positive result will be returned for comparision of, e.g.
   * - [1,2,3] and [1,2,3,4]
   * - [1,1,1] and [1,2,3]
   * */

  function _uniqContentEquals(aIterator, bIterator, stackA, stackB) {
    var a = _arrayFromIterator(aIterator);
    var b = _arrayFromIterator(bIterator);

    function eq(_a, _b) {
      return _equals(_a, _b, stackA.slice(), stackB.slice());
    }

    // if *a* array contains any element that is not included in *b*
    return !_includesWith(function(b, aItem) {
      return !_includesWith(eq, aItem, b);
    }, b, a);
  }

  function _equals(a, b, stackA, stackB) {
    if (_objectIs$1(a, b)) {
      return true;
    }

    var typeA = type(a);

    if (typeA !== type(b)) {
      return false;
    }

    if (a == null || b == null) {
      return false;
    }

    if (typeof a['fantasy-land/equals'] === 'function' || typeof b['fantasy-land/equals'] === 'function') {
      return typeof a['fantasy-land/equals'] === 'function' && a['fantasy-land/equals'](b) &&
        typeof b['fantasy-land/equals'] === 'function' && b['fantasy-land/equals'](a);
    }

    if (typeof a.equals === 'function' || typeof b.equals === 'function') {
      return typeof a.equals === 'function' && a.equals(b) &&
        typeof b.equals === 'function' && b.equals(a);
    }

    switch (typeA) {
      case 'Arguments':
      case 'Array':
      case 'Object':
        if (typeof a.constructor === 'function' &&
          _functionName(a.constructor) === 'Promise') {
          return a === b;
        }
        break;
      case 'Boolean':
      case 'Number':
      case 'String':
        if (!(typeof a === typeof b && _objectIs$1(a.valueOf(), b.valueOf()))) {
          return false;
        }
        break;
      case 'Date':
        if (!_objectIs$1(a.valueOf(), b.valueOf())) {
          return false;
        }
        break;
      case 'Error':
        return a.name === b.name && a.message === b.message;
      case 'RegExp':
        if (!(a.source === b.source &&
            a.global === b.global &&
            a.ignoreCase === b.ignoreCase &&
            a.multiline === b.multiline &&
            a.sticky === b.sticky &&
            a.unicode === b.unicode)) {
          return false;
        }
        break;
    }

    var idx = stackA.length - 1;
    while (idx >= 0) {
      if (stackA[idx] === a) {
        return stackB[idx] === b;
      }
      idx -= 1;
    }

    switch (typeA) {
      case 'Map':
        if (a.size !== b.size) {
          return false;
        }

        return _uniqContentEquals(a.entries(), b.entries(), stackA.concat([a]), stackB.concat([b]));
      case 'Set':
        if (a.size !== b.size) {
          return false;
        }

        return _uniqContentEquals(a.values(), b.values(), stackA.concat([a]), stackB.concat([b]));
      case 'Arguments':
      case 'Array':
      case 'Object':
      case 'Boolean':
      case 'Number':
      case 'String':
      case 'Date':
      case 'Error':
      case 'RegExp':
      case 'Int8Array':
      case 'Uint8Array':
      case 'Uint8ClampedArray':
      case 'Int16Array':
      case 'Uint16Array':
      case 'Int32Array':
      case 'Uint32Array':
      case 'Float32Array':
      case 'Float64Array':
      case 'ArrayBuffer':
        break;
      default:
        // Values of other types are only equal if identical.
        return false;
    }

    var keysA = keys(a);
    if (keysA.length !== keys(b).length) {
      return false;
    }

    var extendedStackA = stackA.concat([a]);
    var extendedStackB = stackB.concat([b]);

    idx = keysA.length - 1;
    while (idx >= 0) {
      var key = keysA[idx];
      if (!(_has(key, b) && _equals(b[key], a[key], extendedStackA, extendedStackB))) {
        return false;
      }
      idx -= 1;
    }
    return true;
  }

  /**
   * Returns `true` if its arguments are equivalent, `false` otherwise. Handles
   * cyclical data structures.
   *
   * Dispatches symmetrically to the `equals` methods of both arguments, if
   * present.
   *
   * @func
   * @memberOf R
   * @since v0.15.0
   * @category Relation
   * @sig a -> b -> Boolean
   * @param {*} a
   * @param {*} b
   * @return {Boolean}
   * @example
   *
   *      R.equals(1, 1); //=> true
   *      R.equals(1, '1'); //=> false
   *      R.equals([1, 2, 3], [1, 2, 3]); //=> true
   *
   *      const a = {}; a.v = a;
   *      const b = {}; b.v = b;
   *      R.equals(a, b); //=> true
   */
  var equals = _curry2(function equals(a, b) {
    return _equals(a, b, [], []);
  });

  function _indexOf(list, a, idx) {
    var inf, item;
    // Array.prototype.indexOf doesn't exist below IE9
    if (typeof list.indexOf === 'function') {
      switch (typeof a) {
        case 'number':
          if (a === 0) {
            // manually crawl the list to distinguish between +0 and -0
            inf = 1 / a;
            while (idx < list.length) {
              item = list[idx];
              if (item === 0 && 1 / item === inf) {
                return idx;
              }
              idx += 1;
            }
            return -1;
          } else if (a !== a) {
            // NaN
            while (idx < list.length) {
              item = list[idx];
              if (typeof item === 'number' && item !== item) {
                return idx;
              }
              idx += 1;
            }
            return -1;
          }
          // non-zero numbers can utilise Set
          return list.indexOf(a, idx);

        // all these types can utilise Set
        case 'string':
        case 'boolean':
        case 'function':
        case 'undefined':
          return list.indexOf(a, idx);

        case 'object':
          if (a === null) {
            // null can utilise Set
            return list.indexOf(a, idx);
          }
      }
    }
    // anything else not covered above, defer to R.equals
    while (idx < list.length) {
      if (equals(list[idx], a)) {
        return idx;
      }
      idx += 1;
    }
    return -1;
  }

  function _includes(a, list) {
    return _indexOf(list, a, 0) >= 0;
  }

  function _quote(s) {
    var escaped = s
      .replace(/\\/g, '\\\\')
      .replace(/[\b]/g, '\\b')  // \b matches word boundary; [\b] matches backspace
      .replace(/\f/g, '\\f')
      .replace(/\n/g, '\\n')
      .replace(/\r/g, '\\r')
      .replace(/\t/g, '\\t')
      .replace(/\v/g, '\\v')
      .replace(/\0/g, '\\0');

    return '"' + escaped.replace(/"/g, '\\"') + '"';
  }

  /**
   * Polyfill from <https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date/toISOString>.
   */
  var pad = function pad(n) { return (n < 10 ? '0' : '') + n; };

  var _toISOString = typeof Date.prototype.toISOString === 'function' ?
    function _toISOString(d) {
      return d.toISOString();
    } :
    function _toISOString(d) {
      return (
        d.getUTCFullYear() + '-' +
        pad(d.getUTCMonth() + 1) + '-' +
        pad(d.getUTCDate()) + 'T' +
        pad(d.getUTCHours()) + ':' +
        pad(d.getUTCMinutes()) + ':' +
        pad(d.getUTCSeconds()) + '.' +
        (d.getUTCMilliseconds() / 1000).toFixed(3).slice(2, 5) + 'Z'
      );
    };

  function _complement(f) {
    return function() {
      return !f.apply(this, arguments);
    };
  }

  function _filter(fn, list) {
    var idx = 0;
    var len = list.length;
    var result = [];

    while (idx < len) {
      if (fn(list[idx])) {
        result[result.length] = list[idx];
      }
      idx += 1;
    }
    return result;
  }

  function _isObject(x) {
    return Object.prototype.toString.call(x) === '[object Object]';
  }

  function XFilter(f, xf) {
    this.xf = xf;
    this.f = f;
  }
  XFilter.prototype['@@transducer/init'] = _xfBase.init;
  XFilter.prototype['@@transducer/result'] = _xfBase.result;
  XFilter.prototype['@@transducer/step'] = function(result, input) {
    return this.f(input) ? this.xf['@@transducer/step'](result, input) : result;
  };

  var _xfilter = _curry2(function _xfilter(f, xf) { return new XFilter(f, xf); });

  /**
   * Takes a predicate and a `Filterable`, and returns a new filterable of the
   * same type containing the members of the given filterable which satisfy the
   * given predicate. Filterable objects include plain objects or any object
   * that has a filter method such as `Array`.
   *
   * Dispatches to the `filter` method of the second argument, if present.
   *
   * Acts as a transducer if a transformer is given in list position.
   *
   * @func
   * @memberOf R
   * @since v0.1.0
   * @category List
   * @sig Filterable f => (a -> Boolean) -> f a -> f a
   * @param {Function} pred
   * @param {Array} filterable
   * @return {Array} Filterable
   * @see R.reject, R.transduce, R.addIndex
   * @example
   *
   *      const isEven = n => n % 2 === 0;
   *
   *      R.filter(isEven, [1, 2, 3, 4]); //=> [2, 4]
   *
   *      R.filter(isEven, {a: 1, b: 2, c: 3, d: 4}); //=> {b: 2, d: 4}
   */
  var filter = _curry2(_dispatchable(['filter'], _xfilter, function(pred, filterable) {
    return (
      _isObject(filterable) ?
        _reduce(function(acc, key) {
          if (pred(filterable[key])) {
            acc[key] = filterable[key];
          }
          return acc;
        }, {}, keys(filterable)) :
      // else
        _filter(pred, filterable)
    );
  }));

  /**
   * The complement of [`filter`](#filter).
   *
   * Acts as a transducer if a transformer is given in list position. Filterable
   * objects include plain objects or any object that has a filter method such
   * as `Array`.
   *
   * @func
   * @memberOf R
   * @since v0.1.0
   * @category List
   * @sig Filterable f => (a -> Boolean) -> f a -> f a
   * @param {Function} pred
   * @param {Array} filterable
   * @return {Array}
   * @see R.filter, R.transduce, R.addIndex
   * @example
   *
   *      const isOdd = (n) => n % 2 === 1;
   *
   *      R.reject(isOdd, [1, 2, 3, 4]); //=> [2, 4]
   *
   *      R.reject(isOdd, {a: 1, b: 2, c: 3, d: 4}); //=> {b: 2, d: 4}
   */
  var reject = _curry2(function reject(pred, filterable) {
    return filter(_complement(pred), filterable);
  });

  function _toString(x, seen) {
    var recur = function recur(y) {
      var xs = seen.concat([x]);
      return _includes(y, xs) ? '<Circular>' : _toString(y, xs);
    };

    //  mapPairs :: (Object, [String]) -> [String]
    var mapPairs = function(obj, keys$$1) {
      return _map(function(k) { return _quote(k) + ': ' + recur(obj[k]); }, keys$$1.slice().sort());
    };

    switch (Object.prototype.toString.call(x)) {
      case '[object Arguments]':
        return '(function() { return arguments; }(' + _map(recur, x).join(', ') + '))';
      case '[object Array]':
        return '[' + _map(recur, x).concat(mapPairs(x, reject(function(k) { return /^\d+$/.test(k); }, keys(x)))).join(', ') + ']';
      case '[object Boolean]':
        return typeof x === 'object' ? 'new Boolean(' + recur(x.valueOf()) + ')' : x.toString();
      case '[object Date]':
        return 'new Date(' + (isNaN(x.valueOf()) ? recur(NaN) : _quote(_toISOString(x))) + ')';
      case '[object Null]':
        return 'null';
      case '[object Number]':
        return typeof x === 'object' ? 'new Number(' + recur(x.valueOf()) + ')' : 1 / x === -Infinity ? '-0' : x.toString(10);
      case '[object String]':
        return typeof x === 'object' ? 'new String(' + recur(x.valueOf()) + ')' : _quote(x);
      case '[object Undefined]':
        return 'undefined';
      default:
        if (typeof x.toString === 'function') {
          var repr = x.toString();
          if (repr !== '[object Object]') {
            return repr;
          }
        }
        return '{' + mapPairs(x, keys(x)).join(', ') + '}';
    }
  }

  /**
   * Returns the string representation of the given value. `eval`'ing the output
   * should result in a value equivalent to the input value. Many of the built-in
   * `toString` methods do not satisfy this requirement.
   *
   * If the given value is an `[object Object]` with a `toString` method other
   * than `Object.prototype.toString`, this method is invoked with no arguments
   * to produce the return value. This means user-defined constructor functions
   * can provide a suitable `toString` method. For example:
   *
   *     function Point(x, y) {
   *       this.x = x;
   *       this.y = y;
   *     }
   *
   *     Point.prototype.toString = function() {
   *       return 'new Point(' + this.x + ', ' + this.y + ')';
   *     };
   *
   *     R.toString(new Point(1, 2)); //=> 'new Point(1, 2)'
   *
   * @func
   * @memberOf R
   * @since v0.14.0
   * @category String
   * @sig * -> String
   * @param {*} val
   * @return {String}
   * @example
   *
   *      R.toString(42); //=> '42'
   *      R.toString('abc'); //=> '"abc"'
   *      R.toString([1, 2, 3]); //=> '[1, 2, 3]'
   *      R.toString({foo: 1, bar: 2, baz: 3}); //=> '{"bar": 2, "baz": 3, "foo": 1}'
   *      R.toString(new Date('2001-02-03T04:05:06Z')); //=> 'new Date("2001-02-03T04:05:06.000Z")'
   */
  var toString$1 = _curry1(function toString(val) { return _toString(val, []); });

  /**
   * Returns the result of concatenating the given lists or strings.
   *
   * Note: `R.concat` expects both arguments to be of the same type,
   * unlike the native `Array.prototype.concat` method. It will throw
   * an error if you `concat` an Array with a non-Array value.
   *
   * Dispatches to the `concat` method of the first argument, if present.
   * Can also concatenate two members of a [fantasy-land
   * compatible semigroup](https://github.com/fantasyland/fantasy-land#semigroup).
   *
   * @func
   * @memberOf R
   * @since v0.1.0
   * @category List
   * @sig [a] -> [a] -> [a]
   * @sig String -> String -> String
   * @param {Array|String} firstList The first list
   * @param {Array|String} secondList The second list
   * @return {Array|String} A list consisting of the elements of `firstList` followed by the elements of
   * `secondList`.
   *
   * @example
   *
   *      R.concat('ABC', 'DEF'); // 'ABCDEF'
   *      R.concat([4, 5, 6], [1, 2, 3]); //=> [4, 5, 6, 1, 2, 3]
   *      R.concat([], []); //=> []
   */
  var concat = _curry2(function concat(a, b) {
    if (_isArray(a)) {
      if (_isArray(b)) {
        return a.concat(b);
      }
      throw new TypeError(toString$1(b) + ' is not an array');
    }
    if (_isString(a)) {
      if (_isString(b)) {
        return a + b;
      }
      throw new TypeError(toString$1(b) + ' is not a string');
    }
    if (a != null && _isFunction(a['fantasy-land/concat'])) {
      return a['fantasy-land/concat'](b);
    }
    if (a != null && _isFunction(a.concat)) {
      return a.concat(b);
    }
    throw new TypeError(toString$1(a) + ' does not have a method named "concat" or "fantasy-land/concat"');
  });

  /**
   * Returns a function, `fn`, which encapsulates `if/else, if/else, ...` logic.
   * `R.cond` takes a list of [predicate, transformer] pairs. All of the arguments
   * to `fn` are applied to each of the predicates in turn until one returns a
   * "truthy" value, at which point `fn` returns the result of applying its
   * arguments to the corresponding transformer. If none of the predicates
   * matches, `fn` returns undefined.
   *
   * @func
   * @memberOf R
   * @since v0.6.0
   * @category Logic
   * @sig [[(*... -> Boolean),(*... -> *)]] -> (*... -> *)
   * @param {Array} pairs A list of [predicate, transformer]
   * @return {Function}
   * @see R.ifElse, R.unless, R.when
   * @example
   *
   *      const fn = R.cond([
   *        [R.equals(0),   R.always('water freezes at 0°C')],
   *        [R.equals(100), R.always('water boils at 100°C')],
   *        [R.T,           temp => 'nothing special happens at ' + temp + '°C']
   *      ]);
   *      fn(0); //=> 'water freezes at 0°C'
   *      fn(50); //=> 'nothing special happens at 50°C'
   *      fn(100); //=> 'water boils at 100°C'
   */
  var cond = _curry1(function cond(pairs) {
    var arity = reduce(
      max,
      0,
      map(function(pair) { return pair[0].length; }, pairs)
    );
    return _arity(arity, function() {
      var idx = 0;
      while (idx < pairs.length) {
        if (pairs[idx][0].apply(this, arguments)) {
          return pairs[idx][1].apply(this, arguments);
        }
        idx += 1;
      }
    });
  });

  /**
   * Wraps a constructor function inside a curried function that can be called
   * with the same arguments and returns the same type. The arity of the function
   * returned is specified to allow using variadic constructor functions.
   *
   * @func
   * @memberOf R
   * @since v0.4.0
   * @category Function
   * @sig Number -> (* -> {*}) -> (* -> {*})
   * @param {Number} n The arity of the constructor function.
   * @param {Function} Fn The constructor function to wrap.
   * @return {Function} A wrapped, curried constructor function.
   * @example
   *
   *      // Variadic Constructor function
   *      function Salad() {
   *        this.ingredients = arguments;
   *      }
   *
   *      Salad.prototype.recipe = function() {
   *        const instructions = R.map(ingredient => 'Add a dollop of ' + ingredient, this.ingredients);
   *        return R.join('\n', instructions);
   *      };
   *
   *      const ThreeLayerSalad = R.constructN(3, Salad);
   *
   *      // Notice we no longer need the 'new' keyword, and the constructor is curried for 3 arguments.
   *      const salad = ThreeLayerSalad('Mayonnaise')('Potato Chips')('Ketchup');
   *
   *      console.log(salad.recipe());
   *      // Add a dollop of Mayonnaise
   *      // Add a dollop of Potato Chips
   *      // Add a dollop of Ketchup
   */
  var constructN = _curry2(function constructN(n, Fn) {
    if (n > 10) {
      throw new Error('Constructor with greater than ten arguments');
    }
    if (n === 0) {
      return function() { return new Fn(); };
    }
    return curry(nAry(n, function($0, $1, $2, $3, $4, $5, $6, $7, $8, $9) {
      switch (arguments.length) {
        case  1: return new Fn($0);
        case  2: return new Fn($0, $1);
        case  3: return new Fn($0, $1, $2);
        case  4: return new Fn($0, $1, $2, $3);
        case  5: return new Fn($0, $1, $2, $3, $4);
        case  6: return new Fn($0, $1, $2, $3, $4, $5);
        case  7: return new Fn($0, $1, $2, $3, $4, $5, $6);
        case  8: return new Fn($0, $1, $2, $3, $4, $5, $6, $7);
        case  9: return new Fn($0, $1, $2, $3, $4, $5, $6, $7, $8);
        case 10: return new Fn($0, $1, $2, $3, $4, $5, $6, $7, $8, $9);
      }
    }));
  });

  /**
   * Wraps a constructor function inside a curried function that can be called
   * with the same arguments and returns the same type.
   *
   * @func
   * @memberOf R
   * @since v0.1.0
   * @category Function
   * @sig (* -> {*}) -> (* -> {*})
   * @param {Function} fn The constructor function to wrap.
   * @return {Function} A wrapped, curried constructor function.
   * @see R.invoker
   * @example
   *
   *      // Constructor function
   *      function Animal(kind) {
   *        this.kind = kind;
   *      };
   *      Animal.prototype.sighting = function() {
   *        return "It's a " + this.kind + "!";
   *      }
   *
   *      const AnimalConstructor = R.construct(Animal)
   *
   *      // Notice we no longer need the 'new' keyword:
   *      AnimalConstructor('Pig'); //=> {"kind": "Pig", "sighting": function (){...}};
   *
   *      const animalTypes = ["Lion", "Tiger", "Bear"];
   *      const animalSighting = R.invoker(0, 'sighting');
   *      const sightNewAnimal = R.compose(animalSighting, AnimalConstructor);
   *      R.map(sightNewAnimal, animalTypes); //=> ["It's a Lion!", "It's a Tiger!", "It's a Bear!"]
   */
  var construct = _curry1(function construct(Fn) {
    return constructN(Fn.length, Fn);
  });

  /**
   * Returns `true` if the specified value is equal, in [`R.equals`](#equals)
   * terms, to at least one element of the given list; `false` otherwise.
   * Works also with strings.
   *
   * @func
   * @memberOf R
   * @since v0.1.0
   * @category List
   * @sig a -> [a] -> Boolean
   * @param {Object} a The item to compare against.
   * @param {Array} list The array to consider.
   * @return {Boolean} `true` if an equivalent item is in the list, `false` otherwise.
   * @see R.includes
   * @deprecated since v0.26.0
   * @example
   *
   *      R.contains(3, [1, 2, 3]); //=> true
   *      R.contains(4, [1, 2, 3]); //=> false
   *      R.contains({ name: 'Fred' }, [{ name: 'Fred' }]); //=> true
   *      R.contains([42], [[42]]); //=> true
   *      R.contains('ba', 'banana'); //=>true
   */
  var contains$1 = _curry2(_includes);

  /**
   * Accepts a converging function and a list of branching functions and returns
   * a new function. The arity of the new function is the same as the arity of
   * the longest branching function. When invoked, this new function is applied
   * to some arguments, and each branching function is applied to those same
   * arguments. The results of each branching function are passed as arguments
   * to the converging function to produce the return value.
   *
   * @func
   * @memberOf R
   * @since v0.4.2
   * @category Function
   * @sig ((x1, x2, ...) -> z) -> [((a, b, ...) -> x1), ((a, b, ...) -> x2), ...] -> (a -> b -> ... -> z)
   * @param {Function} after A function. `after` will be invoked with the return values of
   *        `fn1` and `fn2` as its arguments.
   * @param {Array} functions A list of functions.
   * @return {Function} A new function.
   * @see R.useWith
   * @example
   *
   *      const average = R.converge(R.divide, [R.sum, R.length])
   *      average([1, 2, 3, 4, 5, 6, 7]) //=> 4
   *
   *      const strangeConcat = R.converge(R.concat, [R.toUpper, R.toLower])
   *      strangeConcat("Yodel") //=> "YODELyodel"
   *
   * @symb R.converge(f, [g, h])(a, b) = f(g(a, b), h(a, b))
   */
  var converge = _curry2(function converge(after, fns) {
    return curryN(reduce(max, 0, pluck('length', fns)), function() {
      var args = arguments;
      var context = this;
      return after.apply(context, _map(function(fn) {
        return fn.apply(context, args);
      }, fns));
    });
  });

  function XReduceBy(valueFn, valueAcc, keyFn, xf) {
    this.valueFn = valueFn;
    this.valueAcc = valueAcc;
    this.keyFn = keyFn;
    this.xf = xf;
    this.inputs = {};
  }
  XReduceBy.prototype['@@transducer/init'] = _xfBase.init;
  XReduceBy.prototype['@@transducer/result'] = function(result) {
    var key;
    for (key in this.inputs) {
      if (_has(key, this.inputs)) {
        result = this.xf['@@transducer/step'](result, this.inputs[key]);
        if (result['@@transducer/reduced']) {
          result = result['@@transducer/value'];
          break;
        }
      }
    }
    this.inputs = null;
    return this.xf['@@transducer/result'](result);
  };
  XReduceBy.prototype['@@transducer/step'] = function(result, input) {
    var key = this.keyFn(input);
    this.inputs[key] = this.inputs[key] || [key, this.valueAcc];
    this.inputs[key][1] = this.valueFn(this.inputs[key][1], input);
    return result;
  };

  var _xreduceBy = _curryN(4, [],
    function _xreduceBy(valueFn, valueAcc, keyFn, xf) {
      return new XReduceBy(valueFn, valueAcc, keyFn, xf);
    }
  );

  /**
   * Groups the elements of the list according to the result of calling
   * the String-returning function `keyFn` on each element and reduces the elements
   * of each group to a single value via the reducer function `valueFn`.
   *
   * This function is basically a more general [`groupBy`](#groupBy) function.
   *
   * Acts as a transducer if a transformer is given in list position.
   *
   * @func
   * @memberOf R
   * @since v0.20.0
   * @category List
   * @sig ((a, b) -> a) -> a -> (b -> String) -> [b] -> {String: a}
   * @param {Function} valueFn The function that reduces the elements of each group to a single
   *        value. Receives two values, accumulator for a particular group and the current element.
   * @param {*} acc The (initial) accumulator value for each group.
   * @param {Function} keyFn The function that maps the list's element into a key.
   * @param {Array} list The array to group.
   * @return {Object} An object with the output of `keyFn` for keys, mapped to the output of
   *         `valueFn` for elements which produced that key when passed to `keyFn`.
   * @see R.groupBy, R.reduce
   * @example
   *
   *      const groupNames = (acc, {name}) => acc.concat(name)
   *      const toGrade = ({score}) =>
   *        score < 65 ? 'F' :
   *        score < 70 ? 'D' :
   *        score < 80 ? 'C' :
   *        score < 90 ? 'B' : 'A'
   *
   *      var students = [
   *        {name: 'Abby', score: 83},
   *        {name: 'Bart', score: 62},
   *        {name: 'Curt', score: 88},
   *        {name: 'Dora', score: 92},
   *      ]
   *
   *      reduceBy(groupNames, [], toGrade, students)
   *      //=> {"A": ["Dora"], "B": ["Abby", "Curt"], "F": ["Bart"]}
   */
  var reduceBy = _curryN(4, [], _dispatchable([], _xreduceBy,
    function reduceBy(valueFn, valueAcc, keyFn, list) {
      return _reduce(function(acc, elt) {
        var key = keyFn(elt);
        acc[key] = valueFn(_has(key, acc) ? acc[key] : _clone(valueAcc, [], [], false), elt);
        return acc;
      }, {}, list);
    }));

  /**
   * Counts the elements of a list according to how many match each value of a
   * key generated by the supplied function. Returns an object mapping the keys
   * produced by `fn` to the number of occurrences in the list. Note that all
   * keys are coerced to strings because of how JavaScript objects work.
   *
   * Acts as a transducer if a transformer is given in list position.
   *
   * @func
   * @memberOf R
   * @since v0.1.0
   * @category Relation
   * @sig (a -> String) -> [a] -> {*}
   * @param {Function} fn The function used to map values to keys.
   * @param {Array} list The list to count elements from.
   * @return {Object} An object mapping keys to number of occurrences in the list.
   * @example
   *
   *      const numbers = [1.0, 1.1, 1.2, 2.0, 3.0, 2.2];
   *      R.countBy(Math.floor)(numbers);    //=> {'1': 3, '2': 2, '3': 1}
   *
   *      const letters = ['a', 'b', 'A', 'a', 'B', 'c'];
   *      R.countBy(R.toLower)(letters);   //=> {'a': 3, 'b': 2, 'c': 1}
   */
  var countBy = reduceBy(function(acc, elem) { return acc + 1; }, 0);

  /**
   * Decrements its argument.
   *
   * @func
   * @memberOf R
   * @since v0.9.0
   * @category Math
   * @sig Number -> Number
   * @param {Number} n
   * @return {Number} n - 1
   * @see R.inc
   * @example
   *
   *      R.dec(42); //=> 41
   */
  var dec = add(-1);

  /**
   * Returns the second argument if it is not `null`, `undefined` or `NaN`;
   * otherwise the first argument is returned.
   *
   * @func
   * @memberOf R
   * @since v0.10.0
   * @category Logic
   * @sig a -> b -> a | b
   * @param {a} default The default value.
   * @param {b} val `val` will be returned instead of `default` unless `val` is `null`, `undefined` or `NaN`.
   * @return {*} The second value if it is not `null`, `undefined` or `NaN`, otherwise the default value
   * @example
   *
   *      const defaultTo42 = R.defaultTo(42);
   *
   *      defaultTo42(null);  //=> 42
   *      defaultTo42(undefined);  //=> 42
   *      defaultTo42(false);  //=> false
   *      defaultTo42('Ramda');  //=> 'Ramda'
   *      // parseInt('string') results in NaN
   *      defaultTo42(parseInt('string')); //=> 42
   */
  var defaultTo = _curry2(function defaultTo(d, v) {
    return v == null || v !== v ? d : v;
  });

  /**
   * Makes a descending comparator function out of a function that returns a value
   * that can be compared with `<` and `>`.
   *
   * @func
   * @memberOf R
   * @since v0.23.0
   * @category Function
   * @sig Ord b => (a -> b) -> a -> a -> Number
   * @param {Function} fn A function of arity one that returns a value that can be compared
   * @param {*} a The first item to be compared.
   * @param {*} b The second item to be compared.
   * @return {Number} `-1` if fn(a) > fn(b), `1` if fn(b) > fn(a), otherwise `0`
   * @see R.ascend
   * @example
   *
   *      const byAge = R.descend(R.prop('age'));
   *      const people = [
   *        { name: 'Emma', age: 70 },
   *        { name: 'Peter', age: 78 },
   *        { name: 'Mikhail', age: 62 },
   *      ];
   *      const peopleByOldestFirst = R.sort(byAge, people);
   *        //=> [{ name: 'Peter', age: 78 }, { name: 'Emma', age: 70 }, { name: 'Mikhail', age: 62 }]
   */
  var descend = _curry3(function descend(fn, a, b) {
    var aa = fn(a);
    var bb = fn(b);
    return aa > bb ? -1 : aa < bb ? 1 : 0;
  });

  function _Set() {
    /* globals Set */
    this._nativeSet = typeof Set === 'function' ? new Set() : null;
    this._items = {};
  }

  // until we figure out why jsdoc chokes on this
  // @param item The item to add to the Set
  // @returns {boolean} true if the item did not exist prior, otherwise false
  //
  _Set.prototype.add = function(item) {
    return !hasOrAdd(item, true, this);
  };

  //
  // @param item The item to check for existence in the Set
  // @returns {boolean} true if the item exists in the Set, otherwise false
  //
  _Set.prototype.has = function(item) {
    return hasOrAdd(item, false, this);
  };

  //
  // Combines the logic for checking whether an item is a member of the set and
  // for adding a new item to the set.
  //
  // @param item       The item to check or add to the Set instance.
  // @param shouldAdd  If true, the item will be added to the set if it doesn't
  //                   already exist.
  // @param set        The set instance to check or add to.
  // @return {boolean} true if the item already existed, otherwise false.
  //
  function hasOrAdd(item, shouldAdd, set) {
    var type = typeof item;
    var prevSize, newSize;
    switch (type) {
      case 'string':
      case 'number':
        // distinguish between +0 and -0
        if (item === 0 && 1 / item === -Infinity) {
          if (set._items['-0']) {
            return true;
          } else {
            if (shouldAdd) {
              set._items['-0'] = true;
            }
            return false;
          }
        }
        // these types can all utilise the native Set
        if (set._nativeSet !== null) {
          if (shouldAdd) {
            prevSize = set._nativeSet.size;
            set._nativeSet.add(item);
            newSize = set._nativeSet.size;
            return newSize === prevSize;
          } else {
            return set._nativeSet.has(item);
          }
        } else {
          if (!(type in set._items)) {
            if (shouldAdd) {
              set._items[type] = {};
              set._items[type][item] = true;
            }
            return false;
          } else if (item in set._items[type]) {
            return true;
          } else {
            if (shouldAdd) {
              set._items[type][item] = true;
            }
            return false;
          }
        }

      case 'boolean':
        // set._items['boolean'] holds a two element array
        // representing [ falseExists, trueExists ]
        if (type in set._items) {
          var bIdx = item ? 1 : 0;
          if (set._items[type][bIdx]) {
            return true;
          } else {
            if (shouldAdd) {
              set._items[type][bIdx] = true;
            }
            return false;
          }
        } else {
          if (shouldAdd) {
            set._items[type] = item ? [false, true] : [true, false];
          }
          return false;
        }

      case 'function':
        // compare functions for reference equality
        if (set._nativeSet !== null) {
          if (shouldAdd) {
            prevSize = set._nativeSet.size;
            set._nativeSet.add(item);
            newSize = set._nativeSet.size;
            return newSize === prevSize;
          } else {
            return set._nativeSet.has(item);
          }
        } else {
          if (!(type in set._items)) {
            if (shouldAdd) {
              set._items[type] = [item];
            }
            return false;
          }
          if (!_includes(item, set._items[type])) {
            if (shouldAdd) {
              set._items[type].push(item);
            }
            return false;
          }
          return true;
        }

      case 'undefined':
        if (set._items[type]) {
          return true;
        } else {
          if (shouldAdd) {
            set._items[type] = true;
          }
          return false;
        }

      case 'object':
        if (item === null) {
          if (!set._items['null']) {
            if (shouldAdd) {
              set._items['null'] = true;
            }
            return false;
          }
          return true;
        }
      /* falls through */
      default:
        // reduce the search size of heterogeneous sets by creating buckets
        // for each type.
        type = Object.prototype.toString.call(item);
        if (!(type in set._items)) {
          if (shouldAdd) {
            set._items[type] = [item];
          }
          return false;
        }
        // scan through all previously applied items
        if (!_includes(item, set._items[type])) {
          if (shouldAdd) {
            set._items[type].push(item);
          }
          return false;
        }
        return true;
    }
  }

  /**
   * Finds the set (i.e. no duplicates) of all elements in the first list not
   * contained in the second list. Objects and Arrays are compared in terms of
   * value equality, not reference equality.
   *
   * @func
   * @memberOf R
   * @since v0.1.0
   * @category Relation
   * @sig [*] -> [*] -> [*]
   * @param {Array} list1 The first list.
   * @param {Array} list2 The second list.
   * @return {Array} The elements in `list1` that are not in `list2`.
   * @see R.differenceWith, R.symmetricDifference, R.symmetricDifferenceWith, R.without
   * @example
   *
   *      R.difference([1,2,3,4], [7,6,5,4,3]); //=> [1,2]
   *      R.difference([7,6,5,4,3], [1,2,3,4]); //=> [7,6,5]
   *      R.difference([{a: 1}, {b: 2}], [{a: 1}, {c: 3}]) //=> [{b: 2}]
   */
  var difference = _curry2(function difference(first, second) {
    var out = [];
    var idx = 0;
    var firstLen = first.length;
    var secondLen = second.length;
    var toFilterOut = new _Set();

    for (var i = 0; i < secondLen; i += 1) {
      toFilterOut.add(second[i]);
    }

    while (idx < firstLen) {
      if (toFilterOut.add(first[idx])) {
        out[out.length] = first[idx];
      }
      idx += 1;
    }
    return out;
  });

  /**
   * Finds the set (i.e. no duplicates) of all elements in the first list not
   * contained in the second list. Duplication is determined according to the
   * value returned by applying the supplied predicate to two list elements.
   *
   * @func
   * @memberOf R
   * @since v0.1.0
   * @category Relation
   * @sig ((a, a) -> Boolean) -> [a] -> [a] -> [a]
   * @param {Function} pred A predicate used to test whether two items are equal.
   * @param {Array} list1 The first list.
   * @param {Array} list2 The second list.
   * @return {Array} The elements in `list1` that are not in `list2`.
   * @see R.difference, R.symmetricDifference, R.symmetricDifferenceWith
   * @example
   *
   *      const cmp = (x, y) => x.a === y.a;
   *      const l1 = [{a: 1}, {a: 2}, {a: 3}];
   *      const l2 = [{a: 3}, {a: 4}];
   *      R.differenceWith(cmp, l1, l2); //=> [{a: 1}, {a: 2}]
   */
  var differenceWith = _curry3(function differenceWith(pred, first, second) {
    var out = [];
    var idx = 0;
    var firstLen = first.length;
    while (idx < firstLen) {
      if (!_includesWith(pred, first[idx], second) &&
          !_includesWith(pred, first[idx], out)) {
        out.push(first[idx]);
      }
      idx += 1;
    }
    return out;
  });

  /**
   * Returns a new object that does not contain a `prop` property.
   *
   * @func
   * @memberOf R
   * @since v0.10.0
   * @category Object
   * @sig String -> {k: v} -> {k: v}
   * @param {String} prop The name of the property to dissociate
   * @param {Object} obj The object to clone
   * @return {Object} A new object equivalent to the original but without the specified property
   * @see R.assoc, R.omit
   * @example
   *
   *      R.dissoc('b', {a: 1, b: 2, c: 3}); //=> {a: 1, c: 3}
   */
  var dissoc = _curry2(function dissoc(prop, obj) {
    var result = {};
    for (var p in obj) {
      result[p] = obj[p];
    }
    delete result[prop];
    return result;
  });

  /**
   * Removes the sub-list of `list` starting at index `start` and containing
   * `count` elements. _Note that this is not destructive_: it returns a copy of
   * the list with the changes.
   * <small>No lists have been harmed in the application of this function.</small>
   *
   * @func
   * @memberOf R
   * @since v0.2.2
   * @category List
   * @sig Number -> Number -> [a] -> [a]
   * @param {Number} start The position to start removing elements
   * @param {Number} count The number of elements to remove
   * @param {Array} list The list to remove from
   * @return {Array} A new Array with `count` elements from `start` removed.
   * @see R.without
   * @example
   *
   *      R.remove(2, 3, [1,2,3,4,5,6,7,8]); //=> [1,2,6,7,8]
   */
  var remove = _curry3(function remove(start, count, list) {
    var result = Array.prototype.slice.call(list, 0);
    result.splice(start, count);
    return result;
  });

  /**
   * Returns a new copy of the array with the element at the provided index
   * replaced with the given value.
   *
   * @func
   * @memberOf R
   * @since v0.14.0
   * @category List
   * @sig Number -> a -> [a] -> [a]
   * @param {Number} idx The index to update.
   * @param {*} x The value to exist at the given index of the returned array.
   * @param {Array|Arguments} list The source array-like object to be updated.
   * @return {Array} A copy of `list` with the value at index `idx` replaced with `x`.
   * @see R.adjust
   * @example
   *
   *      R.update(1, '_', ['a', 'b', 'c']);      //=> ['a', '_', 'c']
   *      R.update(-1, '_', ['a', 'b', 'c']);     //=> ['a', 'b', '_']
   * @symb R.update(-1, a, [b, c]) = [b, a]
   * @symb R.update(0, a, [b, c]) = [a, c]
   * @symb R.update(1, a, [b, c]) = [b, a]
   */
  var update = _curry3(function update(idx, x, list) {
    return adjust(idx, always(x), list);
  });

  /**
   * Makes a shallow clone of an object, omitting the property at the given path.
   * Note that this copies and flattens prototype properties onto the new object
   * as well. All non-primitive properties are copied by reference.
   *
   * @func
   * @memberOf R
   * @since v0.11.0
   * @category Object
   * @typedefn Idx = String | Int
   * @sig [Idx] -> {k: v} -> {k: v}
   * @param {Array} path The path to the value to omit
   * @param {Object} obj The object to clone
   * @return {Object} A new object without the property at path
   * @see R.assocPath
   * @example
   *
   *      R.dissocPath(['a', 'b', 'c'], {a: {b: {c: 42}}}); //=> {a: {b: {}}}
   */
  var dissocPath = _curry2(function dissocPath(path, obj) {
    switch (path.length) {
      case 0:
        return obj;
      case 1:
        return _isInteger(path[0]) && _isArray(obj) ? remove(path[0], 1, obj) : dissoc(path[0], obj);
      default:
        var head = path[0];
        var tail = Array.prototype.slice.call(path, 1);
        if (obj[head] == null) {
          return obj;
        } else if (_isInteger(head) && _isArray(obj)) {
          return update(head, dissocPath(tail, obj[head]), obj);
        } else {
          return assoc(head, dissocPath(tail, obj[head]), obj);
        }
    }
  });

  /**
   * Divides two numbers. Equivalent to `a / b`.
   *
   * @func
   * @memberOf R
   * @since v0.1.0
   * @category Math
   * @sig Number -> Number -> Number
   * @param {Number} a The first value.
   * @param {Number} b The second value.
   * @return {Number} The result of `a / b`.
   * @see R.multiply
   * @example
   *
   *      R.divide(71, 100); //=> 0.71
   *
   *      const half = R.divide(R.__, 2);
   *      half(42); //=> 21
   *
   *      const reciprocal = R.divide(1);
   *      reciprocal(4);   //=> 0.25
   */
  var divide = _curry2(function divide(a, b) { return a / b; });

  function XDrop(n, xf) {
    this.xf = xf;
    this.n = n;
  }
  XDrop.prototype['@@transducer/init'] = _xfBase.init;
  XDrop.prototype['@@transducer/result'] = _xfBase.result;
  XDrop.prototype['@@transducer/step'] = function(result, input) {
    if (this.n > 0) {
      this.n -= 1;
      return result;
    }
    return this.xf['@@transducer/step'](result, input);
  };

  var _xdrop = _curry2(function _xdrop(n, xf) { return new XDrop(n, xf); });

  /**
   * Returns all but the first `n` elements of the given list, string, or
   * transducer/transformer (or object with a `drop` method).
   *
   * Dispatches to the `drop` method of the second argument, if present.
   *
   * @func
   * @memberOf R
   * @since v0.1.0
   * @category List
   * @sig Number -> [a] -> [a]
   * @sig Number -> String -> String
   * @param {Number} n
   * @param {*} list
   * @return {*} A copy of list without the first `n` elements
   * @see R.take, R.transduce, R.dropLast, R.dropWhile
   * @example
   *
   *      R.drop(1, ['foo', 'bar', 'baz']); //=> ['bar', 'baz']
   *      R.drop(2, ['foo', 'bar', 'baz']); //=> ['baz']
   *      R.drop(3, ['foo', 'bar', 'baz']); //=> []
   *      R.drop(4, ['foo', 'bar', 'baz']); //=> []
   *      R.drop(3, 'ramda');               //=> 'da'
   */
  var drop = _curry2(_dispatchable(['drop'], _xdrop, function drop(n, xs) {
    return slice(Math.max(0, n), Infinity, xs);
  }));

  function XTake(n, xf) {
    this.xf = xf;
    this.n = n;
    this.i = 0;
  }
  XTake.prototype['@@transducer/init'] = _xfBase.init;
  XTake.prototype['@@transducer/result'] = _xfBase.result;
  XTake.prototype['@@transducer/step'] = function(result, input) {
    this.i += 1;
    var ret = this.n === 0 ? result : this.xf['@@transducer/step'](result, input);
    return this.n >= 0 && this.i >= this.n ? _reduced(ret) : ret;
  };

  var _xtake = _curry2(function _xtake(n, xf) { return new XTake(n, xf); });

  /**
   * Returns the first `n` elements of the given list, string, or
   * transducer/transformer (or object with a `take` method).
   *
   * Dispatches to the `take` method of the second argument, if present.
   *
   * @func
   * @memberOf R
   * @since v0.1.0
   * @category List
   * @sig Number -> [a] -> [a]
   * @sig Number -> String -> String
   * @param {Number} n
   * @param {*} list
   * @return {*}
   * @see R.drop
   * @example
   *
   *      R.take(1, ['foo', 'bar', 'baz']); //=> ['foo']
   *      R.take(2, ['foo', 'bar', 'baz']); //=> ['foo', 'bar']
   *      R.take(3, ['foo', 'bar', 'baz']); //=> ['foo', 'bar', 'baz']
   *      R.take(4, ['foo', 'bar', 'baz']); //=> ['foo', 'bar', 'baz']
   *      R.take(3, 'ramda');               //=> 'ram'
   *
   *      const personnel = [
   *        'Dave Brubeck',
   *        'Paul Desmond',
   *        'Eugene Wright',
   *        'Joe Morello',
   *        'Gerry Mulligan',
   *        'Bob Bates',
   *        'Joe Dodge',
   *        'Ron Crotty'
   *      ];
   *
   *      const takeFive = R.take(5);
   *      takeFive(personnel);
   *      //=> ['Dave Brubeck', 'Paul Desmond', 'Eugene Wright', 'Joe Morello', 'Gerry Mulligan']
   * @symb R.take(-1, [a, b]) = [a, b]
   * @symb R.take(0, [a, b]) = []
   * @symb R.take(1, [a, b]) = [a]
   * @symb R.take(2, [a, b]) = [a, b]
   */
  var take = _curry2(_dispatchable(['take'], _xtake, function take(n, xs) {
    return slice(0, n < 0 ? Infinity : n, xs);
  }));

  function dropLast(n, xs) {
    return take(n < xs.length ? xs.length - n : 0, xs);
  }

  function XDropLast(n, xf) {
    this.xf = xf;
    this.pos = 0;
    this.full = false;
    this.acc = new Array(n);
  }
  XDropLast.prototype['@@transducer/init'] = _xfBase.init;
  XDropLast.prototype['@@transducer/result'] =  function(result) {
    this.acc = null;
    return this.xf['@@transducer/result'](result);
  };
  XDropLast.prototype['@@transducer/step'] = function(result, input) {
    if (this.full) {
      result = this.xf['@@transducer/step'](result, this.acc[this.pos]);
    }
    this.store(input);
    return result;
  };
  XDropLast.prototype.store = function(input) {
    this.acc[this.pos] = input;
    this.pos += 1;
    if (this.pos === this.acc.length) {
      this.pos = 0;
      this.full = true;
    }
  };

  var _xdropLast = _curry2(function _xdropLast(n, xf) { return new XDropLast(n, xf); });

  /**
   * Returns a list containing all but the last `n` elements of the given `list`.
   *
   * Acts as a transducer if a transformer is given in list position.
   *
   * @func
   * @memberOf R
   * @since v0.16.0
   * @category List
   * @sig Number -> [a] -> [a]
   * @sig Number -> String -> String
   * @param {Number} n The number of elements of `list` to skip.
   * @param {Array} list The list of elements to consider.
   * @return {Array} A copy of the list with only the first `list.length - n` elements
   * @see R.takeLast, R.drop, R.dropWhile, R.dropLastWhile
   * @example
   *
   *      R.dropLast(1, ['foo', 'bar', 'baz']); //=> ['foo', 'bar']
   *      R.dropLast(2, ['foo', 'bar', 'baz']); //=> ['foo']
   *      R.dropLast(3, ['foo', 'bar', 'baz']); //=> []
   *      R.dropLast(4, ['foo', 'bar', 'baz']); //=> []
   *      R.dropLast(3, 'ramda');               //=> 'ra'
   */
  var dropLast$1 = _curry2(_dispatchable([], _xdropLast, dropLast));

  function dropLastWhile(pred, xs) {
    var idx = xs.length - 1;
    while (idx >= 0 && pred(xs[idx])) {
      idx -= 1;
    }
    return slice(0, idx + 1, xs);
  }

  function XDropLastWhile(fn, xf) {
    this.f = fn;
    this.retained = [];
    this.xf = xf;
  }
  XDropLastWhile.prototype['@@transducer/init'] = _xfBase.init;
  XDropLastWhile.prototype['@@transducer/result'] = function(result) {
    this.retained = null;
    return this.xf['@@transducer/result'](result);
  };
  XDropLastWhile.prototype['@@transducer/step'] = function(result, input) {
    return this.f(input)
      ? this.retain(result, input)
      : this.flush(result, input);
  };
  XDropLastWhile.prototype.flush = function(result, input) {
    result = _reduce(
      this.xf['@@transducer/step'],
      result,
      this.retained
    );
    this.retained = [];
    return this.xf['@@transducer/step'](result, input);
  };
  XDropLastWhile.prototype.retain = function(result, input) {
    this.retained.push(input);
    return result;
  };

  var _xdropLastWhile = _curry2(function _xdropLastWhile(fn, xf) { return new XDropLastWhile(fn, xf); });

  /**
   * Returns a new list excluding all the tailing elements of a given list which
   * satisfy the supplied predicate function. It passes each value from the right
   * to the supplied predicate function, skipping elements until the predicate
   * function returns a `falsy` value. The predicate function is applied to one argument:
   * *(value)*.
   *
   * Acts as a transducer if a transformer is given in list position.
   *
   * @func
   * @memberOf R
   * @since v0.16.0
   * @category List
   * @sig (a -> Boolean) -> [a] -> [a]
   * @sig (a -> Boolean) -> String -> String
   * @param {Function} predicate The function to be called on each element
   * @param {Array} xs The collection to iterate over.
   * @return {Array} A new array without any trailing elements that return `falsy` values from the `predicate`.
   * @see R.takeLastWhile, R.addIndex, R.drop, R.dropWhile
   * @example
   *
   *      const lteThree = x => x <= 3;
   *
   *      R.dropLastWhile(lteThree, [1, 2, 3, 4, 3, 2, 1]); //=> [1, 2, 3, 4]
   *
   *      R.dropLastWhile(x => x !== 'd' , 'Ramda'); //=> 'Ramd'
   */
  var dropLastWhile$1 = _curry2(_dispatchable([], _xdropLastWhile, dropLastWhile));

  function XDropRepeatsWith(pred, xf) {
    this.xf = xf;
    this.pred = pred;
    this.lastValue = undefined;
    this.seenFirstValue = false;
  }

  XDropRepeatsWith.prototype['@@transducer/init'] = _xfBase.init;
  XDropRepeatsWith.prototype['@@transducer/result'] = _xfBase.result;
  XDropRepeatsWith.prototype['@@transducer/step'] = function(result, input) {
    var sameAsLast = false;
    if (!this.seenFirstValue) {
      this.seenFirstValue = true;
    } else if (this.pred(this.lastValue, input)) {
      sameAsLast = true;
    }
    this.lastValue = input;
    return sameAsLast ? result : this.xf['@@transducer/step'](result, input);
  };

  var _xdropRepeatsWith = _curry2(function _xdropRepeatsWith(pred, xf) { return new XDropRepeatsWith(pred, xf); });

  /**
   * Returns the last element of the given list or string.
   *
   * @func
   * @memberOf R
   * @since v0.1.4
   * @category List
   * @sig [a] -> a | Undefined
   * @sig String -> String
   * @param {*} list
   * @return {*}
   * @see R.init, R.head, R.tail
   * @example
   *
   *      R.last(['fi', 'fo', 'fum']); //=> 'fum'
   *      R.last([]); //=> undefined
   *
   *      R.last('abc'); //=> 'c'
   *      R.last(''); //=> ''
   */
  var last = nth(-1);

  /**
   * Returns a new list without any consecutively repeating elements. Equality is
   * determined by applying the supplied predicate to each pair of consecutive elements. The
   * first element in a series of equal elements will be preserved.
   *
   * Acts as a transducer if a transformer is given in list position.
   *
   * @func
   * @memberOf R
   * @since v0.14.0
   * @category List
   * @sig ((a, a) -> Boolean) -> [a] -> [a]
   * @param {Function} pred A predicate used to test whether two items are equal.
   * @param {Array} list The array to consider.
   * @return {Array} `list` without repeating elements.
   * @see R.transduce
   * @example
   *
   *      const l = [1, -1, 1, 3, 4, -4, -4, -5, 5, 3, 3];
   *      R.dropRepeatsWith(R.eqBy(Math.abs), l); //=> [1, 3, 4, -5, 3]
   */
  var dropRepeatsWith = _curry2(_dispatchable([], _xdropRepeatsWith, function dropRepeatsWith(pred, list) {
    var result = [];
    var idx = 1;
    var len = list.length;
    if (len !== 0) {
      result[0] = list[0];
      while (idx < len) {
        if (!pred(last(result), list[idx])) {
          result[result.length] = list[idx];
        }
        idx += 1;
      }
    }
    return result;
  }));

  /**
   * Returns a new list without any consecutively repeating elements.
   * [`R.equals`](#equals) is used to determine equality.
   *
   * Acts as a transducer if a transformer is given in list position.
   *
   * @func
   * @memberOf R
   * @since v0.14.0
   * @category List
   * @sig [a] -> [a]
   * @param {Array} list The array to consider.
   * @return {Array} `list` without repeating elements.
   * @see R.transduce
   * @example
   *
   *     R.dropRepeats([1, 1, 1, 2, 3, 4, 4, 2, 2]); //=> [1, 2, 3, 4, 2]
   */
  var dropRepeats = _curry1(
    _dispatchable([], _xdropRepeatsWith(equals), dropRepeatsWith(equals))
  );

  function XDropWhile(f, xf) {
    this.xf = xf;
    this.f = f;
  }
  XDropWhile.prototype['@@transducer/init'] = _xfBase.init;
  XDropWhile.prototype['@@transducer/result'] = _xfBase.result;
  XDropWhile.prototype['@@transducer/step'] = function(result, input) {
    if (this.f) {
      if (this.f(input)) {
        return result;
      }
      this.f = null;
    }
    return this.xf['@@transducer/step'](result, input);
  };

  var _xdropWhile = _curry2(function _xdropWhile(f, xf) { return new XDropWhile(f, xf); });

  /**
   * Returns a new list excluding the leading elements of a given list which
   * satisfy the supplied predicate function. It passes each value to the supplied
   * predicate function, skipping elements while the predicate function returns
   * `true`. The predicate function is applied to one argument: *(value)*.
   *
   * Dispatches to the `dropWhile` method of the second argument, if present.
   *
   * Acts as a transducer if a transformer is given in list position.
   *
   * @func
   * @memberOf R
   * @since v0.9.0
   * @category List
   * @sig (a -> Boolean) -> [a] -> [a]
   * @sig (a -> Boolean) -> String -> String
   * @param {Function} fn The function called per iteration.
   * @param {Array} xs The collection to iterate over.
   * @return {Array} A new array.
   * @see R.takeWhile, R.transduce, R.addIndex
   * @example
   *
   *      const lteTwo = x => x <= 2;
   *
   *      R.dropWhile(lteTwo, [1, 2, 3, 4, 3, 2, 1]); //=> [3, 4, 3, 2, 1]
   *
   *      R.dropWhile(x => x !== 'd' , 'Ramda'); //=> 'da'
   */
  var dropWhile = _curry2(_dispatchable(['dropWhile'], _xdropWhile, function dropWhile(pred, xs) {
    var idx = 0;
    var len = xs.length;
    while (idx < len && pred(xs[idx])) {
      idx += 1;
    }
    return slice(idx, Infinity, xs);
  }));

  /**
   * Returns `true` if one or both of its arguments are `true`. Returns `false`
   * if both arguments are `false`.
   *
   * @func
   * @memberOf R
   * @since v0.1.0
   * @category Logic
   * @sig a -> b -> a | b
   * @param {Any} a
   * @param {Any} b
   * @return {Any} the first argument if truthy, otherwise the second argument.
   * @see R.either, R.xor
   * @example
   *
   *      R.or(true, true); //=> true
   *      R.or(true, false); //=> true
   *      R.or(false, true); //=> true
   *      R.or(false, false); //=> false
   */
  var or = _curry2(function or(a, b) {
    return a || b;
  });

  /**
   * A function wrapping calls to the two functions in an `||` operation,
   * returning the result of the first function if it is truth-y and the result
   * of the second function otherwise. Note that this is short-circuited,
   * meaning that the second function will not be invoked if the first returns a
   * truth-y value.
   *
   * In addition to functions, `R.either` also accepts any fantasy-land compatible
   * applicative functor.
   *
   * @func
   * @memberOf R
   * @since v0.12.0
   * @category Logic
   * @sig (*... -> Boolean) -> (*... -> Boolean) -> (*... -> Boolean)
   * @param {Function} f a predicate
   * @param {Function} g another predicate
   * @return {Function} a function that applies its arguments to `f` and `g` and `||`s their outputs together.
   * @see R.or
   * @example
   *
   *      const gt10 = x => x > 10;
   *      const even = x => x % 2 === 0;
   *      const f = R.either(gt10, even);
   *      f(101); //=> true
   *      f(8); //=> true
   *
   *      R.either(Maybe.Just(false), Maybe.Just(55)); // => Maybe.Just(55)
   *      R.either([false, false, 'a'], [11]) // => [11, 11, "a"]
   */
  var either = _curry2(function either(f, g) {
    return _isFunction(f) ?
      function _either() {
        return f.apply(this, arguments) || g.apply(this, arguments);
      } :
      lift(or)(f, g);
  });

  /**
   * Returns the empty value of its argument's type. Ramda defines the empty
   * value of Array (`[]`), Object (`{}`), String (`''`), and Arguments. Other
   * types are supported if they define `<Type>.empty`,
   * `<Type>.prototype.empty` or implement the
   * [FantasyLand Monoid spec](https://github.com/fantasyland/fantasy-land#monoid).
   *
   * Dispatches to the `empty` method of the first argument, if present.
   *
   * @func
   * @memberOf R
   * @since v0.3.0
   * @category Function
   * @sig a -> a
   * @param {*} x
   * @return {*}
   * @example
   *
   *      R.empty(Just(42));      //=> Nothing()
   *      R.empty([1, 2, 3]);     //=> []
   *      R.empty('unicorns');    //=> ''
   *      R.empty({x: 1, y: 2});  //=> {}
   */
  var empty = _curry1(function empty(x) {
    return (
      (x != null && typeof x['fantasy-land/empty'] === 'function')
        ? x['fantasy-land/empty']()
        : (x != null && x.constructor != null && typeof x.constructor['fantasy-land/empty'] === 'function')
          ? x.constructor['fantasy-land/empty']()
          : (x != null && typeof x.empty === 'function')
            ? x.empty()
            : (x != null && x.constructor != null && typeof x.constructor.empty === 'function')
              ? x.constructor.empty()
              : _isArray(x)
                ? []
                : _isString(x)
                  ? ''
                  : _isObject(x)
                    ? {}
                    : _isArguments(x)
                      ? (function() { return arguments; }())
                      : void 0  // else
    );
  });

  /**
   * Returns a new list containing the last `n` elements of the given list.
   * If `n > list.length`, returns a list of `list.length` elements.
   *
   * @func
   * @memberOf R
   * @since v0.16.0
   * @category List
   * @sig Number -> [a] -> [a]
   * @sig Number -> String -> String
   * @param {Number} n The number of elements to return.
   * @param {Array} xs The collection to consider.
   * @return {Array}
   * @see R.dropLast
   * @example
   *
   *      R.takeLast(1, ['foo', 'bar', 'baz']); //=> ['baz']
   *      R.takeLast(2, ['foo', 'bar', 'baz']); //=> ['bar', 'baz']
   *      R.takeLast(3, ['foo', 'bar', 'baz']); //=> ['foo', 'bar', 'baz']
   *      R.takeLast(4, ['foo', 'bar', 'baz']); //=> ['foo', 'bar', 'baz']
   *      R.takeLast(3, 'ramda');               //=> 'mda'
   */
  var takeLast = _curry2(function takeLast(n, xs) {
    return drop(n >= 0 ? xs.length - n : 0, xs);
  });

  /**
   * Checks if a list ends with the provided sublist.
   *
   * Similarly, checks if a string ends with the provided substring.
   *
   * @func
   * @memberOf R
   * @since v0.24.0
   * @category List
   * @sig [a] -> [a] -> Boolean
   * @sig String -> String -> Boolean
   * @param {*} suffix
   * @param {*} list
   * @return {Boolean}
   * @see R.startsWith
   * @example
   *
   *      R.endsWith('c', 'abc')                //=> true
   *      R.endsWith('b', 'abc')                //=> false
   *      R.endsWith(['c'], ['a', 'b', 'c'])    //=> true
   *      R.endsWith(['b'], ['a', 'b', 'c'])    //=> false
   */
  var endsWith = _curry2(function(suffix, list) {
    return equals(takeLast(suffix.length, list), suffix);
  });

  /**
   * Takes a function and two values in its domain and returns `true` if the
   * values map to the same value in the codomain; `false` otherwise.
   *
   * @func
   * @memberOf R
   * @since v0.18.0
   * @category Relation
   * @sig (a -> b) -> a -> a -> Boolean
   * @param {Function} f
   * @param {*} x
   * @param {*} y
   * @return {Boolean}
   * @example
   *
   *      R.eqBy(Math.abs, 5, -5); //=> true
   */
  var eqBy = _curry3(function eqBy(f, x, y) {
    return equals(f(x), f(y));
  });

  /**
   * Reports whether two objects have the same value, in [`R.equals`](#equals)
   * terms, for the specified property. Useful as a curried predicate.
   *
   * @func
   * @memberOf R
   * @since v0.1.0
   * @category Object
   * @sig k -> {k: v} -> {k: v} -> Boolean
   * @param {String} prop The name of the property to compare
   * @param {Object} obj1
   * @param {Object} obj2
   * @return {Boolean}
   *
   * @example
   *
   *      const o1 = { a: 1, b: 2, c: 3, d: 4 };
   *      const o2 = { a: 10, b: 20, c: 3, d: 40 };
   *      R.eqProps('a', o1, o2); //=> false
   *      R.eqProps('c', o1, o2); //=> true
   */
  var eqProps = _curry3(function eqProps(prop, obj1, obj2) {
    return equals(obj1[prop], obj2[prop]);
  });

  /**
   * Creates a new object by recursively evolving a shallow copy of `object`,
   * according to the `transformation` functions. All non-primitive properties
   * are copied by reference.
   *
   * A `transformation` function will not be invoked if its corresponding key
   * does not exist in the evolved object.
   *
   * @func
   * @memberOf R
   * @since v0.9.0
   * @category Object
   * @sig {k: (v -> v)} -> {k: v} -> {k: v}
   * @param {Object} transformations The object specifying transformation functions to apply
   *        to the object.
   * @param {Object} object The object to be transformed.
   * @return {Object} The transformed object.
   * @example
   *
   *      const tomato = {firstName: '  Tomato ', data: {elapsed: 100, remaining: 1400}, id:123};
   *      const transformations = {
   *        firstName: R.trim,
   *        lastName: R.trim, // Will not get invoked.
   *        data: {elapsed: R.add(1), remaining: R.add(-1)}
   *      };
   *      R.evolve(transformations, tomato); //=> {firstName: 'Tomato', data: {elapsed: 101, remaining: 1399}, id:123}
   */
  var evolve = _curry2(function evolve(transformations, object) {
    var result = object instanceof Array ? [] : {};
    var transformation, key, type;
    for (key in object) {
      transformation = transformations[key];
      type = typeof transformation;
      result[key] = type === 'function'
        ? transformation(object[key])
        : transformation && type === 'object'
          ? evolve(transformation, object[key])
          : object[key];
    }
    return result;
  });

  function XFind(f, xf) {
    this.xf = xf;
    this.f = f;
    this.found = false;
  }
  XFind.prototype['@@transducer/init'] = _xfBase.init;
  XFind.prototype['@@transducer/result'] = function(result) {
    if (!this.found) {
      result = this.xf['@@transducer/step'](result, void 0);
    }
    return this.xf['@@transducer/result'](result);
  };
  XFind.prototype['@@transducer/step'] = function(result, input) {
    if (this.f(input)) {
      this.found = true;
      result = _reduced(this.xf['@@transducer/step'](result, input));
    }
    return result;
  };

  var _xfind = _curry2(function _xfind(f, xf) { return new XFind(f, xf); });

  /**
   * Returns the first element of the list which matches the predicate, or
   * `undefined` if no element matches.
   *
   * Dispatches to the `find` method of the second argument, if present.
   *
   * Acts as a transducer if a transformer is given in list position.
   *
   * @func
   * @memberOf R
   * @since v0.1.0
   * @category List
   * @sig (a -> Boolean) -> [a] -> a | undefined
   * @param {Function} fn The predicate function used to determine if the element is the
   *        desired one.
   * @param {Array} list The array to consider.
   * @return {Object} The element found, or `undefined`.
   * @see R.transduce
   * @example
   *
   *      const xs = [{a: 1}, {a: 2}, {a: 3}];
   *      R.find(R.propEq('a', 2))(xs); //=> {a: 2}
   *      R.find(R.propEq('a', 4))(xs); //=> undefined
   */
  var find = _curry2(_dispatchable(['find'], _xfind, function find(fn, list) {
    var idx = 0;
    var len = list.length;
    while (idx < len) {
      if (fn(list[idx])) {
        return list[idx];
      }
      idx += 1;
    }
  }));

  function XFindIndex(f, xf) {
    this.xf = xf;
    this.f = f;
    this.idx = -1;
    this.found = false;
  }
  XFindIndex.prototype['@@transducer/init'] = _xfBase.init;
  XFindIndex.prototype['@@transducer/result'] = function(result) {
    if (!this.found) {
      result = this.xf['@@transducer/step'](result, -1);
    }
    return this.xf['@@transducer/result'](result);
  };
  XFindIndex.prototype['@@transducer/step'] = function(result, input) {
    this.idx += 1;
    if (this.f(input)) {
      this.found = true;
      result = _reduced(this.xf['@@transducer/step'](result, this.idx));
    }
    return result;
  };

  var _xfindIndex = _curry2(function _xfindIndex(f, xf) { return new XFindIndex(f, xf); });

  /**
   * Returns the index of the first element of the list which matches the
   * predicate, or `-1` if no element matches.
   *
   * Acts as a transducer if a transformer is given in list position.
   *
   * @func
   * @memberOf R
   * @since v0.1.1
   * @category List
   * @sig (a -> Boolean) -> [a] -> Number
   * @param {Function} fn The predicate function used to determine if the element is the
   * desired one.
   * @param {Array} list The array to consider.
   * @return {Number} The index of the element found, or `-1`.
   * @see R.transduce
   * @example
   *
   *      const xs = [{a: 1}, {a: 2}, {a: 3}];
   *      R.findIndex(R.propEq('a', 2))(xs); //=> 1
   *      R.findIndex(R.propEq('a', 4))(xs); //=> -1
   */
  var findIndex = _curry2(_dispatchable([], _xfindIndex, function findIndex(fn, list) {
    var idx = 0;
    var len = list.length;
    while (idx < len) {
      if (fn(list[idx])) {
        return idx;
      }
      idx += 1;
    }
    return -1;
  }));

  function XFindLast(f, xf) {
    this.xf = xf;
    this.f = f;
  }
  XFindLast.prototype['@@transducer/init'] = _xfBase.init;
  XFindLast.prototype['@@transducer/result'] = function(result) {
    return this.xf['@@transducer/result'](this.xf['@@transducer/step'](result, this.last));
  };
  XFindLast.prototype['@@transducer/step'] = function(result, input) {
    if (this.f(input)) {
      this.last = input;
    }
    return result;
  };

  var _xfindLast = _curry2(function _xfindLast(f, xf) { return new XFindLast(f, xf); });

  /**
   * Returns the last element of the list which matches the predicate, or
   * `undefined` if no element matches.
   *
   * Acts as a transducer if a transformer is given in list position.
   *
   * @func
   * @memberOf R
   * @since v0.1.1
   * @category List
   * @sig (a -> Boolean) -> [a] -> a | undefined
   * @param {Function} fn The predicate function used to determine if the element is the
   * desired one.
   * @param {Array} list The array to consider.
   * @return {Object} The element found, or `undefined`.
   * @see R.transduce
   * @example
   *
   *      const xs = [{a: 1, b: 0}, {a:1, b: 1}];
   *      R.findLast(R.propEq('a', 1))(xs); //=> {a: 1, b: 1}
   *      R.findLast(R.propEq('a', 4))(xs); //=> undefined
   */
  var findLast = _curry2(_dispatchable([], _xfindLast, function findLast(fn, list) {
    var idx = list.length - 1;
    while (idx >= 0) {
      if (fn(list[idx])) {
        return list[idx];
      }
      idx -= 1;
    }
  }));

  function XFindLastIndex(f, xf) {
    this.xf = xf;
    this.f = f;
    this.idx = -1;
    this.lastIdx = -1;
  }
  XFindLastIndex.prototype['@@transducer/init'] = _xfBase.init;
  XFindLastIndex.prototype['@@transducer/result'] = function(result) {
    return this.xf['@@transducer/result'](this.xf['@@transducer/step'](result, this.lastIdx));
  };
  XFindLastIndex.prototype['@@transducer/step'] = function(result, input) {
    this.idx += 1;
    if (this.f(input)) {
      this.lastIdx = this.idx;
    }
    return result;
  };

  var _xfindLastIndex = _curry2(function _xfindLastIndex(f, xf) { return new XFindLastIndex(f, xf); });

  /**
   * Returns the index of the last element of the list which matches the
   * predicate, or `-1` if no element matches.
   *
   * Acts as a transducer if a transformer is given in list position.
   *
   * @func
   * @memberOf R
   * @since v0.1.1
   * @category List
   * @sig (a -> Boolean) -> [a] -> Number
   * @param {Function} fn The predicate function used to determine if the element is the
   * desired one.
   * @param {Array} list The array to consider.
   * @return {Number} The index of the element found, or `-1`.
   * @see R.transduce
   * @example
   *
   *      const xs = [{a: 1, b: 0}, {a:1, b: 1}];
   *      R.findLastIndex(R.propEq('a', 1))(xs); //=> 1
   *      R.findLastIndex(R.propEq('a', 4))(xs); //=> -1
   */
  var findLastIndex = _curry2(_dispatchable([], _xfindLastIndex, function findLastIndex(fn, list) {
    var idx = list.length - 1;
    while (idx >= 0) {
      if (fn(list[idx])) {
        return idx;
      }
      idx -= 1;
    }
    return -1;
  }));

  /**
   * Returns a new list by pulling every item out of it (and all its sub-arrays)
   * and putting them in a new array, depth-first.
   *
   * @func
   * @memberOf R
   * @since v0.1.0
   * @category List
   * @sig [a] -> [b]
   * @param {Array} list The array to consider.
   * @return {Array} The flattened list.
   * @see R.unnest
   * @example
   *
   *      R.flatten([1, 2, [3, 4], 5, [6, [7, 8, [9, [10, 11], 12]]]]);
   *      //=> [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12]
   */
  var flatten = _curry1(_makeFlat(true));

  /**
   * Returns a new function much like the supplied one, except that the first two
   * arguments' order is reversed.
   *
   * @func
   * @memberOf R
   * @since v0.1.0
   * @category Function
   * @sig ((a, b, c, ...) -> z) -> (b -> a -> c -> ... -> z)
   * @param {Function} fn The function to invoke with its first two parameters reversed.
   * @return {*} The result of invoking `fn` with its first two parameters' order reversed.
   * @example
   *
   *      const mergeThree = (a, b, c) => [].concat(a, b, c);
   *
   *      mergeThree(1, 2, 3); //=> [1, 2, 3]
   *
   *      R.flip(mergeThree)(1, 2, 3); //=> [2, 1, 3]
   * @symb R.flip(f)(a, b, c) = f(b, a, c)
   */
  var flip = _curry1(function flip(fn) {
    return curryN(fn.length, function(a, b) {
      var args = Array.prototype.slice.call(arguments, 0);
      args[0] = b;
      args[1] = a;
      return fn.apply(this, args);
    });
  });

  /**
   * Iterate over an input `list`, calling a provided function `fn` for each
   * element in the list.
   *
   * `fn` receives one argument: *(value)*.
   *
   * Note: `R.forEach` does not skip deleted or unassigned indices (sparse
   * arrays), unlike the native `Array.prototype.forEach` method. For more
   * details on this behavior, see:
   * https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/forEach#Description
   *
   * Also note that, unlike `Array.prototype.forEach`, Ramda's `forEach` returns
   * the original array. In some libraries this function is named `each`.
   *
   * Dispatches to the `forEach` method of the second argument, if present.
   *
   * @func
   * @memberOf R
   * @since v0.1.1
   * @category List
   * @sig (a -> *) -> [a] -> [a]
   * @param {Function} fn The function to invoke. Receives one argument, `value`.
   * @param {Array} list The list to iterate over.
   * @return {Array} The original list.
   * @see R.addIndex
   * @example
   *
   *      const printXPlusFive = x => console.log(x + 5);
   *      R.forEach(printXPlusFive, [1, 2, 3]); //=> [1, 2, 3]
   *      // logs 6
   *      // logs 7
   *      // logs 8
   * @symb R.forEach(f, [a, b, c]) = [a, b, c]
   */
  var forEach = _curry2(_checkForMethod('forEach', function forEach(fn, list) {
    var len = list.length;
    var idx = 0;
    while (idx < len) {
      fn(list[idx]);
      idx += 1;
    }
    return list;
  }));

  /**
   * Iterate over an input `object`, calling a provided function `fn` for each
   * key and value in the object.
   *
   * `fn` receives three argument: *(value, key, obj)*.
   *
   * @func
   * @memberOf R
   * @since v0.23.0
   * @category Object
   * @sig ((a, String, StrMap a) -> Any) -> StrMap a -> StrMap a
   * @param {Function} fn The function to invoke. Receives three argument, `value`, `key`, `obj`.
   * @param {Object} obj The object to iterate over.
   * @return {Object} The original object.
   * @example
   *
   *      const printKeyConcatValue = (value, key) => console.log(key + ':' + value);
   *      R.forEachObjIndexed(printKeyConcatValue, {x: 1, y: 2}); //=> {x: 1, y: 2}
   *      // logs x:1
   *      // logs y:2
   * @symb R.forEachObjIndexed(f, {x: a, y: b}) = {x: a, y: b}
   */
  var forEachObjIndexed = _curry2(function forEachObjIndexed(fn, obj) {
    var keyList = keys(obj);
    var idx = 0;
    while (idx < keyList.length) {
      var key = keyList[idx];
      fn(obj[key], key, obj);
      idx += 1;
    }
    return obj;
  });

  /**
   * Creates a new object from a list key-value pairs. If a key appears in
   * multiple pairs, the rightmost pair is included in the object.
   *
   * @func
   * @memberOf R
   * @since v0.3.0
   * @category List
   * @sig [[k,v]] -> {k: v}
   * @param {Array} pairs An array of two-element arrays that will be the keys and values of the output object.
   * @return {Object} The object made by pairing up `keys` and `values`.
   * @see R.toPairs, R.pair
   * @example
   *
   *      R.fromPairs([['a', 1], ['b', 2], ['c', 3]]); //=> {a: 1, b: 2, c: 3}
   */
  var fromPairs = _curry1(function fromPairs(pairs) {
    var result = {};
    var idx = 0;
    while (idx < pairs.length) {
      result[pairs[idx][0]] = pairs[idx][1];
      idx += 1;
    }
    return result;
  });

  /**
   * Splits a list into sub-lists stored in an object, based on the result of
   * calling a String-returning function on each element, and grouping the
   * results according to values returned.
   *
   * Dispatches to the `groupBy` method of the second argument, if present.
   *
   * Acts as a transducer if a transformer is given in list position.
   *
   * @func
   * @memberOf R
   * @since v0.1.0
   * @category List
   * @sig (a -> String) -> [a] -> {String: [a]}
   * @param {Function} fn Function :: a -> String
   * @param {Array} list The array to group
   * @return {Object} An object with the output of `fn` for keys, mapped to arrays of elements
   *         that produced that key when passed to `fn`.
   * @see R.reduceBy, R.transduce
   * @example
   *
   *      const byGrade = R.groupBy(function(student) {
   *        const score = student.score;
   *        return score < 65 ? 'F' :
   *               score < 70 ? 'D' :
   *               score < 80 ? 'C' :
   *               score < 90 ? 'B' : 'A';
   *      });
   *      const students = [{name: 'Abby', score: 84},
   *                      {name: 'Eddy', score: 58},
   *                      // ...
   *                      {name: 'Jack', score: 69}];
   *      byGrade(students);
   *      // {
   *      //   'A': [{name: 'Dianne', score: 99}],
   *      //   'B': [{name: 'Abby', score: 84}]
   *      //   // ...,
   *      //   'F': [{name: 'Eddy', score: 58}]
   *      // }
   */
  var groupBy = _curry2(_checkForMethod('groupBy', reduceBy(function(acc, item) {
    if (acc == null) {
      acc = [];
    }
    acc.push(item);
    return acc;
  }, null)));

  /**
   * Takes a list and returns a list of lists where each sublist's elements are
   * all satisfied pairwise comparison according to the provided function.
   * Only adjacent elements are passed to the comparison function.
   *
   * @func
   * @memberOf R
   * @since v0.21.0
   * @category List
   * @sig ((a, a) → Boolean) → [a] → [[a]]
   * @param {Function} fn Function for determining whether two given (adjacent)
   *        elements should be in the same group
   * @param {Array} list The array to group. Also accepts a string, which will be
   *        treated as a list of characters.
   * @return {List} A list that contains sublists of elements,
   *         whose concatenations are equal to the original list.
   * @example
   *
   * R.groupWith(R.equals, [0, 1, 1, 2, 3, 5, 8, 13, 21])
   * //=> [[0], [1, 1], [2], [3], [5], [8], [13], [21]]
   *
   * R.groupWith((a, b) => a + 1 === b, [0, 1, 1, 2, 3, 5, 8, 13, 21])
   * //=> [[0, 1], [1, 2, 3], [5], [8], [13], [21]]
   *
   * R.groupWith((a, b) => a % 2 === b % 2, [0, 1, 1, 2, 3, 5, 8, 13, 21])
   * //=> [[0], [1, 1], [2], [3, 5], [8], [13, 21]]
   *
   * R.groupWith(R.eqBy(isVowel), 'aestiou')
   * //=> ['ae', 'st', 'iou']
   */
  var groupWith = _curry2(function(fn, list) {
    var res = [];
    var idx = 0;
    var len = list.length;
    while (idx < len) {
      var nextidx = idx + 1;
      while (nextidx < len && fn(list[nextidx - 1], list[nextidx])) {
        nextidx += 1;
      }
      res.push(list.slice(idx, nextidx));
      idx = nextidx;
    }
    return res;
  });

  /**
   * Returns `true` if the first argument is greater than the second; `false`
   * otherwise.
   *
   * @func
   * @memberOf R
   * @since v0.1.0
   * @category Relation
   * @sig Ord a => a -> a -> Boolean
   * @param {*} a
   * @param {*} b
   * @return {Boolean}
   * @see R.lt
   * @example
   *
   *      R.gt(2, 1); //=> true
   *      R.gt(2, 2); //=> false
   *      R.gt(2, 3); //=> false
   *      R.gt('a', 'z'); //=> false
   *      R.gt('z', 'a'); //=> true
   */
  var gt = _curry2(function gt(a, b) { return a > b; });

  /**
   * Returns `true` if the first argument is greater than or equal to the second;
   * `false` otherwise.
   *
   * @func
   * @memberOf R
   * @since v0.1.0
   * @category Relation
   * @sig Ord a => a -> a -> Boolean
   * @param {Number} a
   * @param {Number} b
   * @return {Boolean}
   * @see R.lte
   * @example
   *
   *      R.gte(2, 1); //=> true
   *      R.gte(2, 2); //=> true
   *      R.gte(2, 3); //=> false
   *      R.gte('a', 'z'); //=> false
   *      R.gte('z', 'a'); //=> true
   */
  var gte = _curry2(function gte(a, b) { return a >= b; });

  /**
   * Returns whether or not a path exists in an object. Only the object's
   * own properties are checked.
   *
   * @func
   * @memberOf R
   * @since v0.26.0
   * @category Object
   * @typedefn Idx = String | Int
   * @sig [Idx] -> {a} -> Boolean
   * @param {Array} path The path to use.
   * @param {Object} obj The object to check the path in.
   * @return {Boolean} Whether the path exists.
   * @see R.has
   * @example
   *
   *      R.hasPath(['a', 'b'], {a: {b: 2}});         // => true
   *      R.hasPath(['a', 'b'], {a: {b: undefined}}); // => true
   *      R.hasPath(['a', 'b'], {a: {c: 2}});         // => false
   *      R.hasPath(['a', 'b'], {});                  // => false
   */
  var hasPath = _curry2(function hasPath(_path, obj) {
    if (_path.length === 0 || isNil(obj)) {
      return false;
    }
    var val = obj;
    var idx = 0;
    while (idx < _path.length) {
      if (!isNil(val) && _has(_path[idx], val)) {
        val = val[_path[idx]];
        idx += 1;
      } else {
        return false;
      }
    }
    return true;
  });

  /**
   * Returns whether or not an object has an own property with the specified name
   *
   * @func
   * @memberOf R
   * @since v0.7.0
   * @category Object
   * @sig s -> {s: x} -> Boolean
   * @param {String} prop The name of the property to check for.
   * @param {Object} obj The object to query.
   * @return {Boolean} Whether the property exists.
   * @example
   *
   *      const hasName = R.has('name');
   *      hasName({name: 'alice'});   //=> true
   *      hasName({name: 'bob'});     //=> true
   *      hasName({});                //=> false
   *
   *      const point = {x: 0, y: 0};
   *      const pointHas = R.has(R.__, point);
   *      pointHas('x');  //=> true
   *      pointHas('y');  //=> true
   *      pointHas('z');  //=> false
   */
  var has = _curry2(function has(prop, obj) {
    return hasPath([prop], obj);
  });

  /**
   * Returns whether or not an object or its prototype chain has a property with
   * the specified name
   *
   * @func
   * @memberOf R
   * @since v0.7.0
   * @category Object
   * @sig s -> {s: x} -> Boolean
   * @param {String} prop The name of the property to check for.
   * @param {Object} obj The object to query.
   * @return {Boolean} Whether the property exists.
   * @example
   *
   *      function Rectangle(width, height) {
   *        this.width = width;
   *        this.height = height;
   *      }
   *      Rectangle.prototype.area = function() {
   *        return this.width * this.height;
   *      };
   *
   *      const square = new Rectangle(2, 2);
   *      R.hasIn('width', square);  //=> true
   *      R.hasIn('area', square);  //=> true
   */
  var hasIn = _curry2(function hasIn(prop, obj) {
    return prop in obj;
  });

  /**
   * Returns true if its arguments are identical, false otherwise. Values are
   * identical if they reference the same memory. `NaN` is identical to `NaN`;
   * `0` and `-0` are not identical.
   *
   * Note this is merely a curried version of ES6 `Object.is`.
   *
   * @func
   * @memberOf R
   * @since v0.15.0
   * @category Relation
   * @sig a -> a -> Boolean
   * @param {*} a
   * @param {*} b
   * @return {Boolean}
   * @example
   *
   *      const o = {};
   *      R.identical(o, o); //=> true
   *      R.identical(1, 1); //=> true
   *      R.identical(1, '1'); //=> false
   *      R.identical([], []); //=> false
   *      R.identical(0, -0); //=> false
   *      R.identical(NaN, NaN); //=> true
   */
  var identical = _curry2(_objectIs$1);

  /**
   * Creates a function that will process either the `onTrue` or the `onFalse`
   * function depending upon the result of the `condition` predicate.
   *
   * @func
   * @memberOf R
   * @since v0.8.0
   * @category Logic
   * @sig (*... -> Boolean) -> (*... -> *) -> (*... -> *) -> (*... -> *)
   * @param {Function} condition A predicate function
   * @param {Function} onTrue A function to invoke when the `condition` evaluates to a truthy value.
   * @param {Function} onFalse A function to invoke when the `condition` evaluates to a falsy value.
   * @return {Function} A new function that will process either the `onTrue` or the `onFalse`
   *                    function depending upon the result of the `condition` predicate.
   * @see R.unless, R.when, R.cond
   * @example
   *
   *      const incCount = R.ifElse(
   *        R.has('count'),
   *        R.over(R.lensProp('count'), R.inc),
   *        R.assoc('count', 1)
   *      );
   *      incCount({});           //=> { count: 1 }
   *      incCount({ count: 1 }); //=> { count: 2 }
   */
  var ifElse = _curry3(function ifElse(condition, onTrue, onFalse) {
    return curryN(Math.max(condition.length, onTrue.length, onFalse.length),
      function _ifElse() {
        return condition.apply(this, arguments) ? onTrue.apply(this, arguments) : onFalse.apply(this, arguments);
      }
    );
  });

  /**
   * Increments its argument.
   *
   * @func
   * @memberOf R
   * @since v0.9.0
   * @category Math
   * @sig Number -> Number
   * @param {Number} n
   * @return {Number} n + 1
   * @see R.dec
   * @example
   *
   *      R.inc(42); //=> 43
   */
  var inc = add(1);

  /**
   * Returns `true` if the specified value is equal, in [`R.equals`](#equals)
   * terms, to at least one element of the given list; `false` otherwise.
   * Works also with strings.
   *
   * @func
   * @memberOf R
   * @since v0.26.0
   * @category List
   * @sig a -> [a] -> Boolean
   * @param {Object} a The item to compare against.
   * @param {Array} list The array to consider.
   * @return {Boolean} `true` if an equivalent item is in the list, `false` otherwise.
   * @see R.any
   * @example
   *
   *      R.includes(3, [1, 2, 3]); //=> true
   *      R.includes(4, [1, 2, 3]); //=> false
   *      R.includes({ name: 'Fred' }, [{ name: 'Fred' }]); //=> true
   *      R.includes([42], [[42]]); //=> true
   *      R.includes('ba', 'banana'); //=>true
   */
  var includes = _curry2(_includes);

  /**
   * Given a function that generates a key, turns a list of objects into an
   * object indexing the objects by the given key. Note that if multiple
   * objects generate the same value for the indexing key only the last value
   * will be included in the generated object.
   *
   * Acts as a transducer if a transformer is given in list position.
   *
   * @func
   * @memberOf R
   * @since v0.19.0
   * @category List
   * @sig (a -> String) -> [{k: v}] -> {k: {k: v}}
   * @param {Function} fn Function :: a -> String
   * @param {Array} array The array of objects to index
   * @return {Object} An object indexing each array element by the given property.
   * @example
   *
   *      const list = [{id: 'xyz', title: 'A'}, {id: 'abc', title: 'B'}];
   *      R.indexBy(R.prop('id'), list);
   *      //=> {abc: {id: 'abc', title: 'B'}, xyz: {id: 'xyz', title: 'A'}}
   */
  var indexBy = reduceBy(function(acc, elem) { return elem; }, null);

  /**
   * Returns the position of the first occurrence of an item in an array, or -1
   * if the item is not included in the array. [`R.equals`](#equals) is used to
   * determine equality.
   *
   * @func
   * @memberOf R
   * @since v0.1.0
   * @category List
   * @sig a -> [a] -> Number
   * @param {*} target The item to find.
   * @param {Array} xs The array to search in.
   * @return {Number} the index of the target, or -1 if the target is not found.
   * @see R.lastIndexOf
   * @example
   *
   *      R.indexOf(3, [1,2,3,4]); //=> 2
   *      R.indexOf(10, [1,2,3,4]); //=> -1
   */
  var indexOf = _curry2(function indexOf(target, xs) {
    return typeof xs.indexOf === 'function' && !_isArray(xs) ?
      xs.indexOf(target) :
      _indexOf(xs, target, 0);
  });

  /**
   * Returns all but the last element of the given list or string.
   *
   * @func
   * @memberOf R
   * @since v0.9.0
   * @category List
   * @sig [a] -> [a]
   * @sig String -> String
   * @param {*} list
   * @return {*}
   * @see R.last, R.head, R.tail
   * @example
   *
   *      R.init([1, 2, 3]);  //=> [1, 2]
   *      R.init([1, 2]);     //=> [1]
   *      R.init([1]);        //=> []
   *      R.init([]);         //=> []
   *
   *      R.init('abc');  //=> 'ab'
   *      R.init('ab');   //=> 'a'
   *      R.init('a');    //=> ''
   *      R.init('');     //=> ''
   */
  var init = slice(0, -1);

  /**
   * Takes a predicate `pred`, a list `xs`, and a list `ys`, and returns a list
   * `xs'` comprising each of the elements of `xs` which is equal to one or more
   * elements of `ys` according to `pred`.
   *
   * `pred` must be a binary function expecting an element from each list.
   *
   * `xs`, `ys`, and `xs'` are treated as sets, semantically, so ordering should
   * not be significant, but since `xs'` is ordered the implementation guarantees
   * that its values are in the same order as they appear in `xs`. Duplicates are
   * not removed, so `xs'` may contain duplicates if `xs` contains duplicates.
   *
   * @func
   * @memberOf R
   * @since v0.24.0
   * @category Relation
   * @sig ((a, b) -> Boolean) -> [a] -> [b] -> [a]
   * @param {Function} pred
   * @param {Array} xs
   * @param {Array} ys
   * @return {Array}
   * @see R.intersection
   * @example
   *
   *      R.innerJoin(
   *        (record, id) => record.id === id,
   *        [{id: 824, name: 'Richie Furay'},
   *         {id: 956, name: 'Dewey Martin'},
   *         {id: 313, name: 'Bruce Palmer'},
   *         {id: 456, name: 'Stephen Stills'},
   *         {id: 177, name: 'Neil Young'}],
   *        [177, 456, 999]
   *      );
   *      //=> [{id: 456, name: 'Stephen Stills'}, {id: 177, name: 'Neil Young'}]
   */
  var innerJoin = _curry3(function innerJoin(pred, xs, ys) {
    return _filter(function(x) { return _includesWith(pred, x, ys); }, xs);
  });

  /**
   * Inserts the supplied element into the list, at the specified `index`. _Note that

   * this is not destructive_: it returns a copy of the list with the changes.
   * <small>No lists have been harmed in the application of this function.</small>
   *
   * @func
   * @memberOf R
   * @since v0.2.2
   * @category List
   * @sig Number -> a -> [a] -> [a]
   * @param {Number} index The position to insert the element
   * @param {*} elt The element to insert into the Array
   * @param {Array} list The list to insert into
   * @return {Array} A new Array with `elt` inserted at `index`.
   * @example
   *
   *      R.insert(2, 'x', [1,2,3,4]); //=> [1,2,'x',3,4]
   */
  var insert = _curry3(function insert(idx, elt, list) {
    idx = idx < list.length && idx >= 0 ? idx : list.length;
    var result = Array.prototype.slice.call(list, 0);
    result.splice(idx, 0, elt);
    return result;
  });

  /**
   * Inserts the sub-list into the list, at the specified `index`. _Note that this is not
   * destructive_: it returns a copy of the list with the changes.
   * <small>No lists have been harmed in the application of this function.</small>
   *
   * @func
   * @memberOf R
   * @since v0.9.0
   * @category List
   * @sig Number -> [a] -> [a] -> [a]
   * @param {Number} index The position to insert the sub-list
   * @param {Array} elts The sub-list to insert into the Array
   * @param {Array} list The list to insert the sub-list into
   * @return {Array} A new Array with `elts` inserted starting at `index`.
   * @example
   *
   *      R.insertAll(2, ['x','y','z'], [1,2,3,4]); //=> [1,2,'x','y','z',3,4]
   */
  var insertAll = _curry3(function insertAll(idx, elts, list) {
    idx = idx < list.length && idx >= 0 ? idx : list.length;
    return [].concat(
      Array.prototype.slice.call(list, 0, idx),
      elts,
      Array.prototype.slice.call(list, idx)
    );
  });

  /**
   * Returns a new list containing only one copy of each element in the original
   * list, based upon the value returned by applying the supplied function to
   * each list element. Prefers the first item if the supplied function produces
   * the same value on two items. [`R.equals`](#equals) is used for comparison.
   *
   * @func
   * @memberOf R
   * @since v0.16.0
   * @category List
   * @sig (a -> b) -> [a] -> [a]
   * @param {Function} fn A function used to produce a value to use during comparisons.
   * @param {Array} list The array to consider.
   * @return {Array} The list of unique items.
   * @example
   *
   *      R.uniqBy(Math.abs, [-1, -5, 2, 10, 1, 2]); //=> [-1, -5, 2, 10]
   */
  var uniqBy = _curry2(function uniqBy(fn, list) {
    var set = new _Set();
    var result = [];
    var idx = 0;
    var appliedItem, item;

    while (idx < list.length) {
      item = list[idx];
      appliedItem = fn(item);
      if (set.add(appliedItem)) {
        result.push(item);
      }
      idx += 1;
    }
    return result;
  });

  /**
   * Returns a new list containing only one copy of each element in the original
   * list. [`R.equals`](#equals) is used to determine equality.
   *
   * @func
   * @memberOf R
   * @since v0.1.0
   * @category List
   * @sig [a] -> [a]
   * @param {Array} list The array to consider.
   * @return {Array} The list of unique items.
   * @example
   *
   *      R.uniq([1, 1, 2, 1]); //=> [1, 2]
   *      R.uniq([1, '1']);     //=> [1, '1']
   *      R.uniq([[42], [42]]); //=> [[42]]
   */
  var uniq = uniqBy(identity);

  /**
   * Combines two lists into a set (i.e. no duplicates) composed of those
   * elements common to both lists.
   *
   * @func
   * @memberOf R
   * @since v0.1.0
   * @category Relation
   * @sig [*] -> [*] -> [*]
   * @param {Array} list1 The first list.
   * @param {Array} list2 The second list.
   * @return {Array} The list of elements found in both `list1` and `list2`.
   * @see R.innerJoin
   * @example
   *
   *      R.intersection([1,2,3,4], [7,6,5,4,3]); //=> [4, 3]
   */
  var intersection = _curry2(function intersection(list1, list2) {
    var lookupList, filteredList;
    if (list1.length > list2.length) {
      lookupList = list1;
      filteredList = list2;
    } else {
      lookupList = list2;
      filteredList = list1;
    }
    return uniq(_filter(flip(_includes)(lookupList), filteredList));
  });

  /**
   * Creates a new list with the separator interposed between elements.
   *
   * Dispatches to the `intersperse` method of the second argument, if present.
   *
   * @func
   * @memberOf R
   * @since v0.14.0
   * @category List
   * @sig a -> [a] -> [a]
   * @param {*} separator The element to add to the list.
   * @param {Array} list The list to be interposed.
   * @return {Array} The new list.
   * @example
   *
   *      R.intersperse('a', ['b', 'n', 'n', 's']); //=> ['b', 'a', 'n', 'a', 'n', 'a', 's']
   */
  var intersperse = _curry2(_checkForMethod('intersperse', function intersperse(separator, list) {
    var out = [];
    var idx = 0;
    var length = list.length;
    while (idx < length) {
      if (idx === length - 1) {
        out.push(list[idx]);
      } else {
        out.push(list[idx], separator);
      }
      idx += 1;
    }
    return out;
  }));

  // Based on https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/Object/assign
  function _objectAssign(target) {
    if (target == null) {
      throw new TypeError('Cannot convert undefined or null to object');
    }

    var output = Object(target);
    var idx = 1;
    var length = arguments.length;
    while (idx < length) {
      var source = arguments[idx];
      if (source != null) {
        for (var nextKey in source) {
          if (_has(nextKey, source)) {
            output[nextKey] = source[nextKey];
          }
        }
      }
      idx += 1;
    }
    return output;
  }

  var _objectAssign$1 = typeof Object.assign === 'function' ? Object.assign : _objectAssign;

  /**
   * Creates an object containing a single key:value pair.
   *
   * @func
   * @memberOf R
   * @since v0.18.0
   * @category Object
   * @sig String -> a -> {String:a}
   * @param {String} key
   * @param {*} val
   * @return {Object}
   * @see R.pair
   * @example
   *
   *      const matchPhrases = R.compose(
   *        R.objOf('must'),
   *        R.map(R.objOf('match_phrase'))
   *      );
   *      matchPhrases(['foo', 'bar', 'baz']); //=> {must: [{match_phrase: 'foo'}, {match_phrase: 'bar'}, {match_phrase: 'baz'}]}
   */
  var objOf = _curry2(function objOf(key, val) {
    var obj = {};
    obj[key] = val;
    return obj;
  });

  var _stepCatArray = {
    '@@transducer/init': Array,
    '@@transducer/step': function(xs, x) {
      xs.push(x);
      return xs;
    },
    '@@transducer/result': _identity
  };
  var _stepCatString = {
    '@@transducer/init': String,
    '@@transducer/step': function(a, b) { return a + b; },
    '@@transducer/result': _identity
  };
  var _stepCatObject = {
    '@@transducer/init': Object,
    '@@transducer/step': function(result, input) {
      return _objectAssign$1(
        result,
        _isArrayLike(input) ? objOf(input[0], input[1]) : input
      );
    },
    '@@transducer/result': _identity
  };

  function _stepCat(obj) {
    if (_isTransformer(obj)) {
      return obj;
    }
    if (_isArrayLike(obj)) {
      return _stepCatArray;
    }
    if (typeof obj === 'string') {
      return _stepCatString;
    }
    if (typeof obj === 'object') {
      return _stepCatObject;
    }
    throw new Error('Cannot create transformer for ' + obj);
  }

  /**
   * Transforms the items of the list with the transducer and appends the
   * transformed items to the accumulator using an appropriate iterator function
   * based on the accumulator type.
   *
   * The accumulator can be an array, string, object or a transformer. Iterated
   * items will be appended to arrays and concatenated to strings. Objects will
   * be merged directly or 2-item arrays will be merged as key, value pairs.
   *
   * The accumulator can also be a transformer object that provides a 2-arity
   * reducing iterator function, step, 0-arity initial value function, init, and
   * 1-arity result extraction function result. The step function is used as the
   * iterator function in reduce. The result function is used to convert the
   * final accumulator into the return type and in most cases is R.identity. The
   * init function is used to provide the initial accumulator.
   *
   * The iteration is performed with [`R.reduce`](#reduce) after initializing the
   * transducer.
   *
   * @func
   * @memberOf R
   * @since v0.12.0
   * @category List
   * @sig a -> (b -> b) -> [c] -> a
   * @param {*} acc The initial accumulator value.
   * @param {Function} xf The transducer function. Receives a transformer and returns a transformer.
   * @param {Array} list The list to iterate over.
   * @return {*} The final, accumulated value.
   * @see R.transduce
   * @example
   *
   *      const numbers = [1, 2, 3, 4];
   *      const transducer = R.compose(R.map(R.add(1)), R.take(2));
   *
   *      R.into([], transducer, numbers); //=> [2, 3]
   *
   *      const intoArray = R.into([]);
   *      intoArray(transducer, numbers); //=> [2, 3]
   */
  var into = _curry3(function into(acc, xf, list) {
    return _isTransformer(acc) ?
      _reduce(xf(acc), acc['@@transducer/init'](), list) :
      _reduce(xf(_stepCat(acc)), _clone(acc, [], [], false), list);
  });

  /**
   * Same as [`R.invertObj`](#invertObj), however this accounts for objects with
   * duplicate values by putting the values into an array.
   *
   * @func
   * @memberOf R
   * @since v0.9.0
   * @category Object
   * @sig {s: x} -> {x: [ s, ... ]}
   * @param {Object} obj The object or array to invert
   * @return {Object} out A new object with keys in an array.
   * @see R.invertObj
   * @example
   *
   *      const raceResultsByFirstName = {
   *        first: 'alice',
   *        second: 'jake',
   *        third: 'alice',
   *      };
   *      R.invert(raceResultsByFirstName);
   *      //=> { 'alice': ['first', 'third'], 'jake':['second'] }
   */
  var invert = _curry1(function invert(obj) {
    var props = keys(obj);
    var len = props.length;
    var idx = 0;
    var out = {};

    while (idx < len) {
      var key = props[idx];
      var val = obj[key];
      var list = _has(val, out) ? out[val] : (out[val] = []);
      list[list.length] = key;
      idx += 1;
    }
    return out;
  });

  /**
   * Returns a new object with the keys of the given object as values, and the
   * values of the given object, which are coerced to strings, as keys. Note
   * that the last key found is preferred when handling the same value.
   *
   * @func
   * @memberOf R
   * @since v0.9.0
   * @category Object
   * @sig {s: x} -> {x: s}
   * @param {Object} obj The object or array to invert
   * @return {Object} out A new object
   * @see R.invert
   * @example
   *
   *      const raceResults = {
   *        first: 'alice',
   *        second: 'jake'
   *      };
   *      R.invertObj(raceResults);
   *      //=> { 'alice': 'first', 'jake':'second' }
   *
   *      // Alternatively:
   *      const raceResults = ['alice', 'jake'];
   *      R.invertObj(raceResults);
   *      //=> { 'alice': '0', 'jake':'1' }
   */
  var invertObj = _curry1(function invertObj(obj) {
    var props = keys(obj);
    var len = props.length;
    var idx = 0;
    var out = {};

    while (idx < len) {
      var key = props[idx];
      out[obj[key]] = key;
      idx += 1;
    }
    return out;
  });

  /**
   * Turns a named method with a specified arity into a function that can be
   * called directly supplied with arguments and a target object.
   *
   * The returned function is curried and accepts `arity + 1` parameters where
   * the final parameter is the target object.
   *
   * @func
   * @memberOf R
   * @since v0.1.0
   * @category Function
   * @sig Number -> String -> (a -> b -> ... -> n -> Object -> *)
   * @param {Number} arity Number of arguments the returned function should take
   *        before the target object.
   * @param {String} method Name of any of the target object's methods to call.
   * @return {Function} A new curried function.
   * @see R.construct
   * @example
   *
   *      const sliceFrom = R.invoker(1, 'slice');
   *      sliceFrom(6, 'abcdefghijklm'); //=> 'ghijklm'
   *      const sliceFrom6 = R.invoker(2, 'slice')(6);
   *      sliceFrom6(8, 'abcdefghijklm'); //=> 'gh'
   *
   *      const dog = {
   *        speak: async () => 'Woof!'
   *      };
   *      const speak = R.invoker(0, 'speak');
   *      speak(dog).then(console.log) //~> 'Woof!'
   *
   * @symb R.invoker(0, 'method')(o) = o['method']()
   * @symb R.invoker(1, 'method')(a, o) = o['method'](a)
   * @symb R.invoker(2, 'method')(a, b, o) = o['method'](a, b)
   */
  var invoker = _curry2(function invoker(arity, method) {
    return curryN(arity + 1, function() {
      var target = arguments[arity];
      if (target != null && _isFunction(target[method])) {
        return target[method].apply(target, Array.prototype.slice.call(arguments, 0, arity));
      }
      throw new TypeError(toString$1(target) + ' does not have a method named "' + method + '"');
    });
  });

  /**
   * See if an object (`val`) is an instance of the supplied constructor. This
   * function will check up the inheritance chain, if any.
   *
   * @func
   * @memberOf R
   * @since v0.3.0
   * @category Type
   * @sig (* -> {*}) -> a -> Boolean
   * @param {Object} ctor A constructor
   * @param {*} val The value to test
   * @return {Boolean}
   * @example
   *
   *      R.is(Object, {}); //=> true
   *      R.is(Number, 1); //=> true
   *      R.is(Object, 1); //=> false
   *      R.is(String, 's'); //=> true
   *      R.is(String, new String('')); //=> true
   *      R.is(Object, new String('')); //=> true
   *      R.is(Object, 's'); //=> false
   *      R.is(Number, {}); //=> false
   */
  var is = _curry2(function is(Ctor, val) {
    return val != null && val.constructor === Ctor || val instanceof Ctor;
  });

  /**
   * Returns `true` if the given value is its type's empty value; `false`
   * otherwise.
   *
   * @func
   * @memberOf R
   * @since v0.1.0
   * @category Logic
   * @sig a -> Boolean
   * @param {*} x
   * @return {Boolean}
   * @see R.empty
   * @example
   *
   *      R.isEmpty([1, 2, 3]);   //=> false
   *      R.isEmpty([]);          //=> true
   *      R.isEmpty('');          //=> true
   *      R.isEmpty(null);        //=> false
   *      R.isEmpty({});          //=> true
   *      R.isEmpty({length: 0}); //=> false
   */
  var isEmpty = _curry1(function isEmpty(x) {
    return x != null && equals(x, empty(x));
  });

  /**
   * Returns a string made by inserting the `separator` between each element and
   * concatenating all the elements into a single string.
   *
   * @func
   * @memberOf R
   * @since v0.1.0
   * @category List
   * @sig String -> [a] -> String
   * @param {Number|String} separator The string used to separate the elements.
   * @param {Array} xs The elements to join into a string.
   * @return {String} str The string made by concatenating `xs` with `separator`.
   * @see R.split
   * @example
   *
   *      const spacer = R.join(' ');
   *      spacer(['a', 2, 3.4]);   //=> 'a 2 3.4'
   *      R.join('|', [1, 2, 3]);    //=> '1|2|3'
   */
  var join = invoker(1, 'join');

  /**
   * juxt applies a list of functions to a list of values.
   *
   * @func
   * @memberOf R
   * @since v0.19.0
   * @category Function
   * @sig [(a, b, ..., m) -> n] -> ((a, b, ..., m) -> [n])
   * @param {Array} fns An array of functions
   * @return {Function} A function that returns a list of values after applying each of the original `fns` to its parameters.
   * @see R.applySpec
   * @example
   *
   *      const getRange = R.juxt([Math.min, Math.max]);
   *      getRange(3, 4, 9, -3); //=> [-3, 9]
   * @symb R.juxt([f, g, h])(a, b) = [f(a, b), g(a, b), h(a, b)]
   */
  var juxt = _curry1(function juxt(fns) {
    return converge(function() { return Array.prototype.slice.call(arguments, 0); }, fns);
  });

  /**
   * Returns a list containing the names of all the properties of the supplied
   * object, including prototype properties.
   * Note that the order of the output array is not guaranteed to be consistent
   * across different JS platforms.
   *
   * @func
   * @memberOf R
   * @since v0.2.0
   * @category Object
   * @sig {k: v} -> [k]
   * @param {Object} obj The object to extract properties from
   * @return {Array} An array of the object's own and prototype properties.
   * @see R.keys, R.valuesIn
   * @example
   *
   *      const F = function() { this.x = 'X'; };
   *      F.prototype.y = 'Y';
   *      const f = new F();
   *      R.keysIn(f); //=> ['x', 'y']
   */
  var keysIn = _curry1(function keysIn(obj) {
    var prop;
    var ks = [];
    for (prop in obj) {
      ks[ks.length] = prop;
    }
    return ks;
  });

  /**
   * Returns the position of the last occurrence of an item in an array, or -1 if
   * the item is not included in the array. [`R.equals`](#equals) is used to
   * determine equality.
   *
   * @func
   * @memberOf R
   * @since v0.1.0
   * @category List
   * @sig a -> [a] -> Number
   * @param {*} target The item to find.
   * @param {Array} xs The array to search in.
   * @return {Number} the index of the target, or -1 if the target is not found.
   * @see R.indexOf
   * @example
   *
   *      R.lastIndexOf(3, [-1,3,3,0,1,2,3,4]); //=> 6
   *      R.lastIndexOf(10, [1,2,3,4]); //=> -1
   */
  var lastIndexOf = _curry2(function lastIndexOf(target, xs) {
    if (typeof xs.lastIndexOf === 'function' && !_isArray(xs)) {
      return xs.lastIndexOf(target);
    } else {
      var idx = xs.length - 1;
      while (idx >= 0) {
        if (equals(xs[idx], target)) {
          return idx;
        }
        idx -= 1;
      }
      return -1;
    }
  });

  function _isNumber(x) {
    return Object.prototype.toString.call(x) === '[object Number]';
  }

  /**
   * Returns the number of elements in the array by returning `list.length`.
   *
   * @func
   * @memberOf R
   * @since v0.3.0
   * @category List
   * @sig [a] -> Number
   * @param {Array} list The array to inspect.
   * @return {Number} The length of the array.
   * @example
   *
   *      R.length([]); //=> 0
   *      R.length([1, 2, 3]); //=> 3
   */
  var length = _curry1(function length(list) {
    return list != null && _isNumber(list.length) ? list.length : NaN;
  });

  /**
   * Returns a lens for the given getter and setter functions. The getter "gets"
   * the value of the focus; the setter "sets" the value of the focus. The setter
   * should not mutate the data structure.
   *
   * @func
   * @memberOf R
   * @since v0.8.0
   * @category Object
   * @typedefn Lens s a = Functor f => (a -> f a) -> s -> f s
   * @sig (s -> a) -> ((a, s) -> s) -> Lens s a
   * @param {Function} getter
   * @param {Function} setter
   * @return {Lens}
   * @see R.view, R.set, R.over, R.lensIndex, R.lensProp
   * @example
   *
   *      const xLens = R.lens(R.prop('x'), R.assoc('x'));
   *
   *      R.view(xLens, {x: 1, y: 2});            //=> 1
   *      R.set(xLens, 4, {x: 1, y: 2});          //=> {x: 4, y: 2}
   *      R.over(xLens, R.negate, {x: 1, y: 2});  //=> {x: -1, y: 2}
   */
  var lens = _curry2(function lens(getter, setter) {
    return function(toFunctorFn) {
      return function(target) {
        return map(
          function(focus) {
            return setter(focus, target);
          },
          toFunctorFn(getter(target))
        );
      };
    };
  });

  /**
   * Returns a lens whose focus is the specified index.
   *
   * @func
   * @memberOf R
   * @since v0.14.0
   * @category Object
   * @typedefn Lens s a = Functor f => (a -> f a) -> s -> f s
   * @sig Number -> Lens s a
   * @param {Number} n
   * @return {Lens}
   * @see R.view, R.set, R.over, R.nth
   * @example
   *
   *      const headLens = R.lensIndex(0);
   *
   *      R.view(headLens, ['a', 'b', 'c']);            //=> 'a'
   *      R.set(headLens, 'x', ['a', 'b', 'c']);        //=> ['x', 'b', 'c']
   *      R.over(headLens, R.toUpper, ['a', 'b', 'c']); //=> ['A', 'b', 'c']
   */
  var lensIndex = _curry1(function lensIndex(n) {
    return lens(nth(n), update(n));
  });

  /**
   * Returns a lens whose focus is the specified path.
   *
   * @func
   * @memberOf R
   * @since v0.19.0
   * @category Object
   * @typedefn Idx = String | Int
   * @typedefn Lens s a = Functor f => (a -> f a) -> s -> f s
   * @sig [Idx] -> Lens s a
   * @param {Array} path The path to use.
   * @return {Lens}
   * @see R.view, R.set, R.over
   * @example
   *
   *      const xHeadYLens = R.lensPath(['x', 0, 'y']);
   *
   *      R.view(xHeadYLens, {x: [{y: 2, z: 3}, {y: 4, z: 5}]});
   *      //=> 2
   *      R.set(xHeadYLens, 1, {x: [{y: 2, z: 3}, {y: 4, z: 5}]});
   *      //=> {x: [{y: 1, z: 3}, {y: 4, z: 5}]}
   *      R.over(xHeadYLens, R.negate, {x: [{y: 2, z: 3}, {y: 4, z: 5}]});
   *      //=> {x: [{y: -2, z: 3}, {y: 4, z: 5}]}
   */
  var lensPath = _curry1(function lensPath(p) {
    return lens(path(p), assocPath(p));
  });

  /**
   * Returns a lens whose focus is the specified property.
   *
   * @func
   * @memberOf R
   * @since v0.14.0
   * @category Object
   * @typedefn Lens s a = Functor f => (a -> f a) -> s -> f s
   * @sig String -> Lens s a
   * @param {String} k
   * @return {Lens}
   * @see R.view, R.set, R.over
   * @example
   *
   *      const xLens = R.lensProp('x');
   *
   *      R.view(xLens, {x: 1, y: 2});            //=> 1
   *      R.set(xLens, 4, {x: 1, y: 2});          //=> {x: 4, y: 2}
   *      R.over(xLens, R.negate, {x: 1, y: 2});  //=> {x: -1, y: 2}
   */
  var lensProp = _curry1(function lensProp(k) {
    return lens(prop(k), assoc(k));
  });

  /**
   * Returns `true` if the first argument is less than the second; `false`
   * otherwise.
   *
   * @func
   * @memberOf R
   * @since v0.1.0
   * @category Relation
   * @sig Ord a => a -> a -> Boolean
   * @param {*} a
   * @param {*} b
   * @return {Boolean}
   * @see R.gt
   * @example
   *
   *      R.lt(2, 1); //=> false
   *      R.lt(2, 2); //=> false
   *      R.lt(2, 3); //=> true
   *      R.lt('a', 'z'); //=> true
   *      R.lt('z', 'a'); //=> false
   */
  var lt = _curry2(function lt(a, b) { return a < b; });

  /**
   * Returns `true` if the first argument is less than or equal to the second;
   * `false` otherwise.
   *
   * @func
   * @memberOf R
   * @since v0.1.0
   * @category Relation
   * @sig Ord a => a -> a -> Boolean
   * @param {Number} a
   * @param {Number} b
   * @return {Boolean}
   * @see R.gte
   * @example
   *
   *      R.lte(2, 1); //=> false
   *      R.lte(2, 2); //=> true
   *      R.lte(2, 3); //=> true
   *      R.lte('a', 'z'); //=> true
   *      R.lte('z', 'a'); //=> false
   */
  var lte = _curry2(function lte(a, b) { return a <= b; });

  /**
   * The `mapAccum` function behaves like a combination of map and reduce; it
   * applies a function to each element of a list, passing an accumulating
   * parameter from left to right, and returning a final value of this
   * accumulator together with the new list.
   *
   * The iterator function receives two arguments, *acc* and *value*, and should
   * return a tuple *[acc, value]*.
   *
   * @func
   * @memberOf R
   * @since v0.10.0
   * @category List
   * @sig ((acc, x) -> (acc, y)) -> acc -> [x] -> (acc, [y])
   * @param {Function} fn The function to be called on every element of the input `list`.
   * @param {*} acc The accumulator value.
   * @param {Array} list The list to iterate over.
   * @return {*} The final, accumulated value.
   * @see R.scan, R.addIndex, R.mapAccumRight
   * @example
   *
   *      const digits = ['1', '2', '3', '4'];
   *      const appender = (a, b) => [a + b, a + b];
   *
   *      R.mapAccum(appender, 0, digits); //=> ['01234', ['01', '012', '0123', '01234']]
   * @symb R.mapAccum(f, a, [b, c, d]) = [
   *   f(f(f(a, b)[0], c)[0], d)[0],
   *   [
   *     f(a, b)[1],
   *     f(f(a, b)[0], c)[1],
   *     f(f(f(a, b)[0], c)[0], d)[1]
   *   ]
   * ]
   */
  var mapAccum = _curry3(function mapAccum(fn, acc, list) {
    var idx = 0;
    var len = list.length;
    var result = [];
    var tuple = [acc];
    while (idx < len) {
      tuple = fn(tuple[0], list[idx]);
      result[idx] = tuple[1];
      idx += 1;
    }
    return [tuple[0], result];
  });

  /**
   * The `mapAccumRight` function behaves like a combination of map and reduce; it
   * applies a function to each element of a list, passing an accumulating
   * parameter from right to left, and returning a final value of this
   * accumulator together with the new list.
   *
   * Similar to [`mapAccum`](#mapAccum), except moves through the input list from
   * the right to the left.
   *
   * The iterator function receives two arguments, *acc* and *value*, and should
   * return a tuple *[acc, value]*.
   *
   * @func
   * @memberOf R
   * @since v0.10.0
   * @category List
   * @sig ((acc, x) -> (acc, y)) -> acc -> [x] -> (acc, [y])
   * @param {Function} fn The function to be called on every element of the input `list`.
   * @param {*} acc The accumulator value.
   * @param {Array} list The list to iterate over.
   * @return {*} The final, accumulated value.
   * @see R.addIndex, R.mapAccum
   * @example
   *
   *      const digits = ['1', '2', '3', '4'];
   *      const appender = (a, b) => [b + a, b + a];
   *
   *      R.mapAccumRight(appender, 5, digits); //=> ['12345', ['12345', '2345', '345', '45']]
   * @symb R.mapAccumRight(f, a, [b, c, d]) = [
   *   f(f(f(a, d)[0], c)[0], b)[0],
   *   [
   *     f(a, d)[1],
   *     f(f(a, d)[0], c)[1],
   *     f(f(f(a, d)[0], c)[0], b)[1]
   *   ]
   * ]
   */
  var mapAccumRight = _curry3(function mapAccumRight(fn, acc, list) {
    var idx = list.length - 1;
    var result = [];
    var tuple = [acc];
    while (idx >= 0) {
      tuple = fn(tuple[0], list[idx]);
      result[idx] = tuple[1];
      idx -= 1;
    }
    return [tuple[0], result];
  });

  /**
   * An Object-specific version of [`map`](#map). The function is applied to three
   * arguments: *(value, key, obj)*. If only the value is significant, use
   * [`map`](#map) instead.
   *
   * @func
   * @memberOf R
   * @since v0.9.0
   * @category Object
   * @sig ((*, String, Object) -> *) -> Object -> Object
   * @param {Function} fn
   * @param {Object} obj
   * @return {Object}
   * @see R.map
   * @example
   *
   *      const xyz = { x: 1, y: 2, z: 3 };
   *      const prependKeyAndDouble = (num, key, obj) => key + (num * 2);
   *
   *      R.mapObjIndexed(prependKeyAndDouble, xyz); //=> { x: 'x2', y: 'y4', z: 'z6' }
   */
  var mapObjIndexed = _curry2(function mapObjIndexed(fn, obj) {
    return _reduce(function(acc, key) {
      acc[key] = fn(obj[key], key, obj);
      return acc;
    }, {}, keys(obj));
  });

  /**
   * Tests a regular expression against a String. Note that this function will
   * return an empty array when there are no matches. This differs from
   * [`String.prototype.match`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/match)
   * which returns `null` when there are no matches.
   *
   * @func
   * @memberOf R
   * @since v0.1.0
   * @category String
   * @sig RegExp -> String -> [String | Undefined]
   * @param {RegExp} rx A regular expression.
   * @param {String} str The string to match against
   * @return {Array} The list of matches or empty array.
   * @see R.test
   * @example
   *
   *      R.match(/([a-z]a)/g, 'bananas'); //=> ['ba', 'na', 'na']
   *      R.match(/a/, 'b'); //=> []
   *      R.match(/a/, null); //=> TypeError: null does not have a method named "match"
   */
  var match = _curry2(function match(rx, str) {
    return str.match(rx) || [];
  });

  /**
   * `mathMod` behaves like the modulo operator should mathematically, unlike the
   * `%` operator (and by extension, [`R.modulo`](#modulo)). So while
   * `-17 % 5` is `-2`, `mathMod(-17, 5)` is `3`. `mathMod` requires Integer
   * arguments, and returns NaN when the modulus is zero or negative.
   *
   * @func
   * @memberOf R
   * @since v0.3.0
   * @category Math
   * @sig Number -> Number -> Number
   * @param {Number} m The dividend.
   * @param {Number} p the modulus.
   * @return {Number} The result of `b mod a`.
   * @see R.modulo
   * @example
   *
   *      R.mathMod(-17, 5);  //=> 3
   *      R.mathMod(17, 5);   //=> 2
   *      R.mathMod(17, -5);  //=> NaN
   *      R.mathMod(17, 0);   //=> NaN
   *      R.mathMod(17.2, 5); //=> NaN
   *      R.mathMod(17, 5.3); //=> NaN
   *
   *      const clock = R.mathMod(R.__, 12);
   *      clock(15); //=> 3
   *      clock(24); //=> 0
   *
   *      const seventeenMod = R.mathMod(17);
   *      seventeenMod(3);  //=> 2
   *      seventeenMod(4);  //=> 1
   *      seventeenMod(10); //=> 7
   */
  var mathMod = _curry2(function mathMod(m, p) {
    if (!_isInteger(m)) { return NaN; }
    if (!_isInteger(p) || p < 1) { return NaN; }
    return ((m % p) + p) % p;
  });

  /**
   * Takes a function and two values, and returns whichever value produces the
   * larger result when passed to the provided function.
   *
   * @func
   * @memberOf R
   * @since v0.8.0
   * @category Relation
   * @sig Ord b => (a -> b) -> a -> a -> a
   * @param {Function} f
   * @param {*} a
   * @param {*} b
   * @return {*}
   * @see R.max, R.minBy
   * @example
   *
   *      //  square :: Number -> Number
   *      const square = n => n * n;
   *
   *      R.maxBy(square, -3, 2); //=> -3
   *
   *      R.reduce(R.maxBy(square), 0, [3, -5, 4, 1, -2]); //=> -5
   *      R.reduce(R.maxBy(square), 0, []); //=> 0
   */
  var maxBy = _curry3(function maxBy(f, a, b) {
    return f(b) > f(a) ? b : a;
  });

  /**
   * Adds together all the elements of a list.
   *
   * @func
   * @memberOf R
   * @since v0.1.0
   * @category Math
   * @sig [Number] -> Number
   * @param {Array} list An array of numbers
   * @return {Number} The sum of all the numbers in the list.
   * @see R.reduce
   * @example
   *
   *      R.sum([2,4,6,8,100,1]); //=> 121
   */
  var sum = reduce(add, 0);

  /**
   * Returns the mean of the given list of numbers.
   *
   * @func
   * @memberOf R
   * @since v0.14.0
   * @category Math
   * @sig [Number] -> Number
   * @param {Array} list
   * @return {Number}
   * @see R.median
   * @example
   *
   *      R.mean([2, 7, 9]); //=> 6
   *      R.mean([]); //=> NaN
   */
  var mean = _curry1(function mean(list) {
    return sum(list) / list.length;
  });

  /**
   * Returns the median of the given list of numbers.
   *
   * @func
   * @memberOf R
   * @since v0.14.0
   * @category Math
   * @sig [Number] -> Number
   * @param {Array} list
   * @return {Number}
   * @see R.mean
   * @example
   *
   *      R.median([2, 9, 7]); //=> 7
   *      R.median([7, 2, 10, 9]); //=> 8
   *      R.median([]); //=> NaN
   */
  var median = _curry1(function median(list) {
    var len = list.length;
    if (len === 0) {
      return NaN;
    }
    var width = 2 - len % 2;
    var idx = (len - width) / 2;
    return mean(Array.prototype.slice.call(list, 0).sort(function(a, b) {
      return a < b ? -1 : a > b ? 1 : 0;
    }).slice(idx, idx + width));
  });

  /**
   * Creates a new function that, when invoked, caches the result of calling `fn`
   * for a given argument set and returns the result. Subsequent calls to the
   * memoized `fn` with the same argument set will not result in an additional
   * call to `fn`; instead, the cached result for that set of arguments will be
   * returned.
   *
   *
   * @func
   * @memberOf R
   * @since v0.24.0
   * @category Function
   * @sig (*... -> String) -> (*... -> a) -> (*... -> a)
   * @param {Function} fn The function to generate the cache key.
   * @param {Function} fn The function to memoize.
   * @return {Function} Memoized version of `fn`.
   * @example
   *
   *      let count = 0;
   *      const factorial = R.memoizeWith(R.identity, n => {
   *        count += 1;
   *        return R.product(R.range(1, n + 1));
   *      });
   *      factorial(5); //=> 120
   *      factorial(5); //=> 120
   *      factorial(5); //=> 120
   *      count; //=> 1
   */
  var memoizeWith = _curry2(function memoizeWith(mFn, fn) {
    var cache = {};
    return _arity(fn.length, function() {
      var key = mFn.apply(this, arguments);
      if (!_has(key, cache)) {
        cache[key] = fn.apply(this, arguments);
      }
      return cache[key];
    });
  });

  /**
   * Create a new object with the own properties of the first object merged with
   * the own properties of the second object. If a key exists in both objects,
   * the value from the second object will be used.
   *
   * @func
   * @memberOf R
   * @since v0.1.0
   * @category Object
   * @sig {k: v} -> {k: v} -> {k: v}
   * @param {Object} l
   * @param {Object} r
   * @return {Object}
   * @see R.mergeRight, R.mergeDeepRight, R.mergeWith, R.mergeWithKey
   * @deprecated since v0.26.0
   * @example
   *
   *      R.merge({ 'name': 'fred', 'age': 10 }, { 'age': 40 });
   *      //=> { 'name': 'fred', 'age': 40 }
   *
   *      const withDefaults = R.merge({x: 0, y: 0});
   *      withDefaults({y: 2}); //=> {x: 0, y: 2}
   * @symb R.merge(a, b) = {...a, ...b}
   */
  var merge = _curry2(function merge(l, r) {
    return _objectAssign$1({}, l, r);
  });

  /**
   * Merges a list of objects together into one object.
   *
   * @func
   * @memberOf R
   * @since v0.10.0
   * @category List
   * @sig [{k: v}] -> {k: v}
   * @param {Array} list An array of objects
   * @return {Object} A merged object.
   * @see R.reduce
   * @example
   *
   *      R.mergeAll([{foo:1},{bar:2},{baz:3}]); //=> {foo:1,bar:2,baz:3}
   *      R.mergeAll([{foo:1},{foo:2},{bar:2}]); //=> {foo:2,bar:2}
   * @symb R.mergeAll([{ x: 1 }, { y: 2 }, { z: 3 }]) = { x: 1, y: 2, z: 3 }
   */
  var mergeAll = _curry1(function mergeAll(list) {
    return _objectAssign$1.apply(null, [{}].concat(list));
  });

  /**
   * Creates a new object with the own properties of the two provided objects. If
   * a key exists in both objects, the provided function is applied to the key
   * and the values associated with the key in each object, with the result being
   * used as the value associated with the key in the returned object.
   *
   * @func
   * @memberOf R
   * @since v0.19.0
   * @category Object
   * @sig ((String, a, a) -> a) -> {a} -> {a} -> {a}
   * @param {Function} fn
   * @param {Object} l
   * @param {Object} r
   * @return {Object}
   * @see R.mergeDeepWithKey, R.merge, R.mergeWith
   * @example
   *
   *      let concatValues = (k, l, r) => k == 'values' ? R.concat(l, r) : r
   *      R.mergeWithKey(concatValues,
   *                     { a: true, thing: 'foo', values: [10, 20] },
   *                     { b: true, thing: 'bar', values: [15, 35] });
   *      //=> { a: true, b: true, thing: 'bar', values: [10, 20, 15, 35] }
   * @symb R.mergeWithKey(f, { x: 1, y: 2 }, { y: 5, z: 3 }) = { x: 1, y: f('y', 2, 5), z: 3 }
   */
  var mergeWithKey = _curry3(function mergeWithKey(fn, l, r) {
    var result = {};
    var k;

    for (k in l) {
      if (_has(k, l)) {
        result[k] = _has(k, r) ? fn(k, l[k], r[k]) : l[k];
      }
    }

    for (k in r) {
      if (_has(k, r) && !(_has(k, result))) {
        result[k] = r[k];
      }
    }

    return result;
  });

  /**
   * Creates a new object with the own properties of the two provided objects.
   * If a key exists in both objects:
   * - and both associated values are also objects then the values will be
   *   recursively merged.
   * - otherwise the provided function is applied to the key and associated values
   *   using the resulting value as the new value associated with the key.
   * If a key only exists in one object, the value will be associated with the key
   * of the resulting object.
   *
   * @func
   * @memberOf R
   * @since v0.24.0
   * @category Object
   * @sig ((String, a, a) -> a) -> {a} -> {a} -> {a}
   * @param {Function} fn
   * @param {Object} lObj
   * @param {Object} rObj
   * @return {Object}
   * @see R.mergeWithKey, R.mergeDeepWith
   * @example
   *
   *      let concatValues = (k, l, r) => k == 'values' ? R.concat(l, r) : r
   *      R.mergeDeepWithKey(concatValues,
   *                         { a: true, c: { thing: 'foo', values: [10, 20] }},
   *                         { b: true, c: { thing: 'bar', values: [15, 35] }});
   *      //=> { a: true, b: true, c: { thing: 'bar', values: [10, 20, 15, 35] }}
   */
  var mergeDeepWithKey = _curry3(function mergeDeepWithKey(fn, lObj, rObj) {
    return mergeWithKey(function(k, lVal, rVal) {
      if (_isObject(lVal) && _isObject(rVal)) {
        return mergeDeepWithKey(fn, lVal, rVal);
      } else {
        return fn(k, lVal, rVal);
      }
    }, lObj, rObj);
  });

  /**
   * Creates a new object with the own properties of the first object merged with
   * the own properties of the second object. If a key exists in both objects:
   * - and both values are objects, the two values will be recursively merged
   * - otherwise the value from the first object will be used.
   *
   * @func
   * @memberOf R
   * @since v0.24.0
   * @category Object
   * @sig {a} -> {a} -> {a}
   * @param {Object} lObj
   * @param {Object} rObj
   * @return {Object}
   * @see R.merge, R.mergeDeepRight, R.mergeDeepWith, R.mergeDeepWithKey
   * @example
   *
   *      R.mergeDeepLeft({ name: 'fred', age: 10, contact: { email: 'moo@example.com' }},
   *                      { age: 40, contact: { email: 'baa@example.com' }});
   *      //=> { name: 'fred', age: 10, contact: { email: 'moo@example.com' }}
   */
  var mergeDeepLeft = _curry2(function mergeDeepLeft(lObj, rObj) {
    return mergeDeepWithKey(function(k, lVal, rVal) {
      return lVal;
    }, lObj, rObj);
  });

  /**
   * Creates a new object with the own properties of the first object merged with
   * the own properties of the second object. If a key exists in both objects:
   * - and both values are objects, the two values will be recursively merged
   * - otherwise the value from the second object will be used.
   *
   * @func
   * @memberOf R
   * @since v0.24.0
   * @category Object
   * @sig {a} -> {a} -> {a}
   * @param {Object} lObj
   * @param {Object} rObj
   * @return {Object}
   * @see R.merge, R.mergeDeepLeft, R.mergeDeepWith, R.mergeDeepWithKey
   * @example
   *
   *      R.mergeDeepRight({ name: 'fred', age: 10, contact: { email: 'moo@example.com' }},
   *                       { age: 40, contact: { email: 'baa@example.com' }});
   *      //=> { name: 'fred', age: 40, contact: { email: 'baa@example.com' }}
   */
  var mergeDeepRight = _curry2(function mergeDeepRight(lObj, rObj) {
    return mergeDeepWithKey(function(k, lVal, rVal) {
      return rVal;
    }, lObj, rObj);
  });

  /**
   * Creates a new object with the own properties of the two provided objects.
   * If a key exists in both objects:
   * - and both associated values are also objects then the values will be
   *   recursively merged.
   * - otherwise the provided function is applied to associated values using the
   *   resulting value as the new value associated with the key.
   * If a key only exists in one object, the value will be associated with the key
   * of the resulting object.
   *
   * @func
   * @memberOf R
   * @since v0.24.0
   * @category Object
   * @sig ((a, a) -> a) -> {a} -> {a} -> {a}
   * @param {Function} fn
   * @param {Object} lObj
   * @param {Object} rObj
   * @return {Object}
   * @see R.mergeWith, R.mergeDeepWithKey
   * @example
   *
   *      R.mergeDeepWith(R.concat,
   *                      { a: true, c: { values: [10, 20] }},
   *                      { b: true, c: { values: [15, 35] }});
   *      //=> { a: true, b: true, c: { values: [10, 20, 15, 35] }}
   */
  var mergeDeepWith = _curry3(function mergeDeepWith(fn, lObj, rObj) {
    return mergeDeepWithKey(function(k, lVal, rVal) {
      return fn(lVal, rVal);
    }, lObj, rObj);
  });

  /**
   * Create a new object with the own properties of the first object merged with
   * the own properties of the second object. If a key exists in both objects,
   * the value from the first object will be used.
   *
   * @func
   * @memberOf R
   * @since v0.26.0
   * @category Object
   * @sig {k: v} -> {k: v} -> {k: v}
   * @param {Object} l
   * @param {Object} r
   * @return {Object}
   * @see R.mergeRight, R.mergeDeepLeft, R.mergeWith, R.mergeWithKey
   * @example
   *
   *      R.mergeLeft({ 'age': 40 }, { 'name': 'fred', 'age': 10 });
   *      //=> { 'name': 'fred', 'age': 40 }
   *
   *      const resetToDefault = R.mergeLeft({x: 0});
   *      resetToDefault({x: 5, y: 2}); //=> {x: 0, y: 2}
   * @symb R.mergeLeft(a, b) = {...b, ...a}
   */
  var mergeLeft = _curry2(function mergeLeft(l, r) {
    return _objectAssign$1({}, r, l);
  });

  /**
   * Create a new object with the own properties of the first object merged with
   * the own properties of the second object. If a key exists in both objects,
   * the value from the second object will be used.
   *
   * @func
   * @memberOf R
   * @since v0.26.0
   * @category Object
   * @sig {k: v} -> {k: v} -> {k: v}
   * @param {Object} l
   * @param {Object} r
   * @return {Object}
   * @see R.mergeLeft, R.mergeDeepRight, R.mergeWith, R.mergeWithKey
   * @example
   *
   *      R.mergeRight({ 'name': 'fred', 'age': 10 }, { 'age': 40 });
   *      //=> { 'name': 'fred', 'age': 40 }
   *
   *      const withDefaults = R.mergeRight({x: 0, y: 0});
   *      withDefaults({y: 2}); //=> {x: 0, y: 2}
   * @symb R.mergeRight(a, b) = {...a, ...b}
   */
  var mergeRight = _curry2(function mergeRight(l, r) {
    return _objectAssign$1({}, l, r);
  });

  /**
   * Creates a new object with the own properties of the two provided objects. If
   * a key exists in both objects, the provided function is applied to the values
   * associated with the key in each object, with the result being used as the
   * value associated with the key in the returned object.
   *
   * @func
   * @memberOf R
   * @since v0.19.0
   * @category Object
   * @sig ((a, a) -> a) -> {a} -> {a} -> {a}
   * @param {Function} fn
   * @param {Object} l
   * @param {Object} r
   * @return {Object}
   * @see R.mergeDeepWith, R.merge, R.mergeWithKey
   * @example
   *
   *      R.mergeWith(R.concat,
   *                  { a: true, values: [10, 20] },
   *                  { b: true, values: [15, 35] });
   *      //=> { a: true, b: true, values: [10, 20, 15, 35] }
   */
  var mergeWith = _curry3(function mergeWith(fn, l, r) {
    return mergeWithKey(function(_, _l, _r) {
      return fn(_l, _r);
    }, l, r);
  });

  /**
   * Returns the smaller of its two arguments.
   *
   * @func
   * @memberOf R
   * @since v0.1.0
   * @category Relation
   * @sig Ord a => a -> a -> a
   * @param {*} a
   * @param {*} b
   * @return {*}
   * @see R.minBy, R.max
   * @example
   *
   *      R.min(789, 123); //=> 123
   *      R.min('a', 'b'); //=> 'a'
   */
  var min = _curry2(function min(a, b) { return b < a ? b : a; });

  /**
   * Takes a function and two values, and returns whichever value produces the
   * smaller result when passed to the provided function.
   *
   * @func
   * @memberOf R
   * @since v0.8.0
   * @category Relation
   * @sig Ord b => (a -> b) -> a -> a -> a
   * @param {Function} f
   * @param {*} a
   * @param {*} b
   * @return {*}
   * @see R.min, R.maxBy
   * @example
   *
   *      //  square :: Number -> Number
   *      const square = n => n * n;
   *
   *      R.minBy(square, -3, 2); //=> 2
   *
   *      R.reduce(R.minBy(square), Infinity, [3, -5, 4, 1, -2]); //=> 1
   *      R.reduce(R.minBy(square), Infinity, []); //=> Infinity
   */
  var minBy = _curry3(function minBy(f, a, b) {
    return f(b) < f(a) ? b : a;
  });

  /**
   * Divides the first parameter by the second and returns the remainder. Note
   * that this function preserves the JavaScript-style behavior for modulo. For
   * mathematical modulo see [`mathMod`](#mathMod).
   *
   * @func
   * @memberOf R
   * @since v0.1.1
   * @category Math
   * @sig Number -> Number -> Number
   * @param {Number} a The value to the divide.
   * @param {Number} b The pseudo-modulus
   * @return {Number} The result of `b % a`.
   * @see R.mathMod
   * @example
   *
   *      R.modulo(17, 3); //=> 2
   *      // JS behavior:
   *      R.modulo(-17, 3); //=> -2
   *      R.modulo(17, -3); //=> 2
   *
   *      const isOdd = R.modulo(R.__, 2);
   *      isOdd(42); //=> 0
   *      isOdd(21); //=> 1
   */
  var modulo = _curry2(function modulo(a, b) { return a % b; });

  /**
   * Move an item, at index `from`, to index `to`, in a list of elements.
   * A new list will be created containing the new elements order.
   *
   * @func
   * @memberOf R
   * @since v0.27.1
   * @category List
   * @sig Number -> Number -> [a] -> [a]
   * @param {Number} from The source index
   * @param {Number} to The destination index
   * @param {Array} list The list which will serve to realise the move
   * @return {Array} The new list reordered
   * @example
   *
   *      R.move(0, 2, ['a', 'b', 'c', 'd', 'e', 'f']); //=> ['b', 'c', 'a', 'd', 'e', 'f']
   *      R.move(-1, 0, ['a', 'b', 'c', 'd', 'e', 'f']); //=> ['f', 'a', 'b', 'c', 'd', 'e'] list rotation
   */
  var move = _curry3(function(from, to, list) {
    var length = list.length;
    var result = list.slice();
    var positiveFrom = from < 0 ? length + from : from;
    var positiveTo = to < 0 ? length + to : to;
    var item = result.splice(positiveFrom, 1);

    return positiveFrom < 0 || positiveFrom >= list.length
        || positiveTo   < 0 || positiveTo   >= list.length
      ? list
      : []
        .concat(result.slice(0, positiveTo))
        .concat(item)
        .concat(result.slice(positiveTo, list.length));
  });

  /**
   * Multiplies two numbers. Equivalent to `a * b` but curried.
   *
   * @func
   * @memberOf R
   * @since v0.1.0
   * @category Math
   * @sig Number -> Number -> Number
   * @param {Number} a The first value.
   * @param {Number} b The second value.
   * @return {Number} The result of `a * b`.
   * @see R.divide
   * @example
   *
   *      const double = R.multiply(2);
   *      const triple = R.multiply(3);
   *      double(3);       //=>  6
   *      triple(4);       //=> 12
   *      R.multiply(2, 5);  //=> 10
   */
  var multiply = _curry2(function multiply(a, b) { return a * b; });

  /**
   * Negates its argument.
   *
   * @func
   * @memberOf R
   * @since v0.9.0
   * @category Math
   * @sig Number -> Number
   * @param {Number} n
   * @return {Number}
   * @example
   *
   *      R.negate(42); //=> -42
   */
  var negate = _curry1(function negate(n) { return -n; });

  /**
   * Returns `true` if no elements of the list match the predicate, `false`
   * otherwise.
   *
   * Dispatches to the `all` method of the second argument, if present.
   *
   * Acts as a transducer if a transformer is given in list position.
   *
   * @func
   * @memberOf R
   * @since v0.12.0
   * @category List
   * @sig (a -> Boolean) -> [a] -> Boolean
   * @param {Function} fn The predicate function.
   * @param {Array} list The array to consider.
   * @return {Boolean} `true` if the predicate is not satisfied by every element, `false` otherwise.
   * @see R.all, R.any
   * @example
   *
   *      const isEven = n => n % 2 === 0;
   *      const isOdd = n => n % 2 === 1;
   *
   *      R.none(isEven, [1, 3, 5, 7, 9, 11]); //=> true
   *      R.none(isOdd, [1, 3, 5, 7, 8, 11]); //=> false
   */
  var none = _curry2(function none(fn, input) {
    return all(_complement(fn), input);
  });

  /**
   * Returns a function which returns its nth argument.
   *
   * @func
   * @memberOf R
   * @since v0.9.0
   * @category Function
   * @sig Number -> *... -> *
   * @param {Number} n
   * @return {Function}
   * @example
   *
   *      R.nthArg(1)('a', 'b', 'c'); //=> 'b'
   *      R.nthArg(-1)('a', 'b', 'c'); //=> 'c'
   * @symb R.nthArg(-1)(a, b, c) = c
   * @symb R.nthArg(0)(a, b, c) = a
   * @symb R.nthArg(1)(a, b, c) = b
   */
  var nthArg = _curry1(function nthArg(n) {
    var arity = n < 0 ? 1 : n + 1;
    return curryN(arity, function() {
      return nth(n, arguments);
    });
  });

  /**
   * `o` is a curried composition function that returns a unary function.
   * Like [`compose`](#compose), `o` performs right-to-left function composition.
   * Unlike [`compose`](#compose), the rightmost function passed to `o` will be
   * invoked with only one argument. Also, unlike [`compose`](#compose), `o` is
   * limited to accepting only 2 unary functions. The name o was chosen because
   * of its similarity to the mathematical composition operator ∘.
   *
   * @func
   * @memberOf R
   * @since v0.24.0
   * @category Function
   * @sig (b -> c) -> (a -> b) -> a -> c
   * @param {Function} f
   * @param {Function} g
   * @return {Function}
   * @see R.compose, R.pipe
   * @example
   *
   *      const classyGreeting = name => "The name's " + name.last + ", " + name.first + " " + name.last
   *      const yellGreeting = R.o(R.toUpper, classyGreeting);
   *      yellGreeting({first: 'James', last: 'Bond'}); //=> "THE NAME'S BOND, JAMES BOND"
   *
   *      R.o(R.multiply(10), R.add(10))(-4) //=> 60
   *
   * @symb R.o(f, g, x) = f(g(x))
   */
  var o = _curry3(function o(f, g, x) {
    return f(g(x));
  });

  function _of(x) { return [x]; }

  /**
   * Returns a singleton array containing the value provided.
   *
   * Note this `of` is different from the ES6 `of`; See
   * https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/of
   *
   * @func
   * @memberOf R
   * @since v0.3.0
   * @category Function
   * @sig a -> [a]
   * @param {*} x any value
   * @return {Array} An array wrapping `x`.
   * @example
   *
   *      R.of(null); //=> [null]
   *      R.of([42]); //=> [[42]]
   */
  var of = _curry1(_of);

  /**
   * Returns a partial copy of an object omitting the keys specified.
   *
   * @func
   * @memberOf R
   * @since v0.1.0
   * @category Object
   * @sig [String] -> {String: *} -> {String: *}
   * @param {Array} names an array of String property names to omit from the new object
   * @param {Object} obj The object to copy from
   * @return {Object} A new object with properties from `names` not on it.
   * @see R.pick
   * @example
   *
   *      R.omit(['a', 'd'], {a: 1, b: 2, c: 3, d: 4}); //=> {b: 2, c: 3}
   */
  var omit = _curry2(function omit(names, obj) {
    var result = {};
    var index = {};
    var idx = 0;
    var len = names.length;

    while (idx < len) {
      index[names[idx]] = 1;
      idx += 1;
    }

    for (var prop in obj) {
      if (!index.hasOwnProperty(prop)) {
        result[prop] = obj[prop];
      }
    }
    return result;
  });

  /**
   * Accepts a function `fn` and returns a function that guards invocation of
   * `fn` such that `fn` can only ever be called once, no matter how many times
   * the returned function is invoked. The first value calculated is returned in
   * subsequent invocations.
   *
   * @func
   * @memberOf R
   * @since v0.1.0
   * @category Function
   * @sig (a... -> b) -> (a... -> b)
   * @param {Function} fn The function to wrap in a call-only-once wrapper.
   * @return {Function} The wrapped function.
   * @example
   *
   *      const addOneOnce = R.once(x => x + 1);
   *      addOneOnce(10); //=> 11
   *      addOneOnce(addOneOnce(50)); //=> 11
   */
  var once = _curry1(function once(fn) {
    var called = false;
    var result;
    return _arity(fn.length, function() {
      if (called) {
        return result;
      }
      called = true;
      result = fn.apply(this, arguments);
      return result;
    });
  });

  function _assertPromise(name, p) {
    if (p == null || !_isFunction(p.then)) {
      throw new TypeError('`' + name + '` expected a Promise, received ' + _toString(p, []));
    }
  }

  /**
   * Returns the result of applying the onFailure function to the value inside
   * a failed promise. This is useful for handling rejected promises
   * inside function compositions.
   *
   * @func
   * @memberOf R
   * @since v0.26.0
   * @category Function
   * @sig (e -> b) -> (Promise e a) -> (Promise e b)
   * @sig (e -> (Promise f b)) -> (Promise e a) -> (Promise f b)
   * @param {Function} onFailure The function to apply. Can return a value or a promise of a value.
   * @param {Promise} p
   * @return {Promise} The result of calling `p.then(null, onFailure)`
   * @see R.then
   * @example
   *
   *      var failedFetch = (id) => Promise.reject('bad ID');
   *      var useDefault = () => ({ firstName: 'Bob', lastName: 'Loblaw' })
   *
   *      //recoverFromFailure :: String -> Promise ({firstName, lastName})
   *      var recoverFromFailure = R.pipe(
   *        failedFetch,
   *        R.otherwise(useDefault),
   *        R.then(R.pick(['firstName', 'lastName'])),
   *      );
   *      recoverFromFailure(12345).then(console.log)
   */
  var otherwise = _curry2(function otherwise(f, p) {
    _assertPromise('otherwise', p);

    return p.then(null, f);
  });

  // `Identity` is a functor that holds a single value, where `map` simply
  // transforms the held value with the provided function.
  var Identity = function(x) {
    return {value: x, map: function(f) { return Identity(f(x)); }};
  };


  /**
   * Returns the result of "setting" the portion of the given data structure
   * focused by the given lens to the result of applying the given function to
   * the focused value.
   *
   * @func
   * @memberOf R
   * @since v0.16.0
   * @category Object
   * @typedefn Lens s a = Functor f => (a -> f a) -> s -> f s
   * @sig Lens s a -> (a -> a) -> s -> s
   * @param {Lens} lens
   * @param {*} v
   * @param {*} x
   * @return {*}
   * @see R.prop, R.lensIndex, R.lensProp
   * @example
   *
   *      const headLens = R.lensIndex(0);
   *
   *      R.over(headLens, R.toUpper, ['foo', 'bar', 'baz']); //=> ['FOO', 'bar', 'baz']
   */
  var over = _curry3(function over(lens, f, x) {
    // The value returned by the getter function is first transformed with `f`,
    // then set as the value of an `Identity`. This is then mapped over with the
    // setter function of the lens.
    return lens(function(y) { return Identity(f(y)); })(x).value;
  });

  /**
   * Takes two arguments, `fst` and `snd`, and returns `[fst, snd]`.
   *
   * @func
   * @memberOf R
   * @since v0.18.0
   * @category List
   * @sig a -> b -> (a,b)
   * @param {*} fst
   * @param {*} snd
   * @return {Array}
   * @see R.objOf, R.of
   * @example
   *
   *      R.pair('foo', 'bar'); //=> ['foo', 'bar']
   */
  var pair = _curry2(function pair(fst, snd) { return [fst, snd]; });

  function _createPartialApplicator(concat) {
    return _curry2(function(fn, args) {
      return _arity(Math.max(0, fn.length - args.length), function() {
        return fn.apply(this, concat(args, arguments));
      });
    });
  }

  /**
   * Takes a function `f` and a list of arguments, and returns a function `g`.
   * When applied, `g` returns the result of applying `f` to the arguments
   * provided initially followed by the arguments provided to `g`.
   *
   * @func
   * @memberOf R
   * @since v0.10.0
   * @category Function
   * @sig ((a, b, c, ..., n) -> x) -> [a, b, c, ...] -> ((d, e, f, ..., n) -> x)
   * @param {Function} f
   * @param {Array} args
   * @return {Function}
   * @see R.partialRight, R.curry
   * @example
   *
   *      const multiply2 = (a, b) => a * b;
   *      const double = R.partial(multiply2, [2]);
   *      double(2); //=> 4
   *
   *      const greet = (salutation, title, firstName, lastName) =>
   *        salutation + ', ' + title + ' ' + firstName + ' ' + lastName + '!';
   *
   *      const sayHello = R.partial(greet, ['Hello']);
   *      const sayHelloToMs = R.partial(sayHello, ['Ms.']);
   *      sayHelloToMs('Jane', 'Jones'); //=> 'Hello, Ms. Jane Jones!'
   * @symb R.partial(f, [a, b])(c, d) = f(a, b, c, d)
   */
  var partial = _createPartialApplicator(_concat);

  /**
   * Takes a function `f` and a list of arguments, and returns a function `g`.
   * When applied, `g` returns the result of applying `f` to the arguments
   * provided to `g` followed by the arguments provided initially.
   *
   * @func
   * @memberOf R
   * @since v0.10.0
   * @category Function
   * @sig ((a, b, c, ..., n) -> x) -> [d, e, f, ..., n] -> ((a, b, c, ...) -> x)
   * @param {Function} f
   * @param {Array} args
   * @return {Function}
   * @see R.partial
   * @example
   *
   *      const greet = (salutation, title, firstName, lastName) =>
   *        salutation + ', ' + title + ' ' + firstName + ' ' + lastName + '!';
   *
   *      const greetMsJaneJones = R.partialRight(greet, ['Ms.', 'Jane', 'Jones']);
   *
   *      greetMsJaneJones('Hello'); //=> 'Hello, Ms. Jane Jones!'
   * @symb R.partialRight(f, [a, b])(c, d) = f(c, d, a, b)
   */
  var partialRight = _createPartialApplicator(flip(_concat));

  /**
   * Takes a predicate and a list or other `Filterable` object and returns the
   * pair of filterable objects of the same type of elements which do and do not
   * satisfy, the predicate, respectively. Filterable objects include plain objects or any object
   * that has a filter method such as `Array`.
   *
   * @func
   * @memberOf R
   * @since v0.1.4
   * @category List
   * @sig Filterable f => (a -> Boolean) -> f a -> [f a, f a]
   * @param {Function} pred A predicate to determine which side the element belongs to.
   * @param {Array} filterable the list (or other filterable) to partition.
   * @return {Array} An array, containing first the subset of elements that satisfy the
   *         predicate, and second the subset of elements that do not satisfy.
   * @see R.filter, R.reject
   * @example
   *
   *      R.partition(R.includes('s'), ['sss', 'ttt', 'foo', 'bars']);
   *      // => [ [ 'sss', 'bars' ],  [ 'ttt', 'foo' ] ]
   *
   *      R.partition(R.includes('s'), { a: 'sss', b: 'ttt', foo: 'bars' });
   *      // => [ { a: 'sss', foo: 'bars' }, { b: 'ttt' }  ]
   */
  var partition = juxt([filter, reject]);

  /**
   * Determines whether a nested path on an object has a specific value, in
   * [`R.equals`](#equals) terms. Most likely used to filter a list.
   *
   * @func
   * @memberOf R
   * @since v0.7.0
   * @category Relation
   * @typedefn Idx = String | Int
   * @sig [Idx] -> a -> {a} -> Boolean
   * @param {Array} path The path of the nested property to use
   * @param {*} val The value to compare the nested property with
   * @param {Object} obj The object to check the nested property in
   * @return {Boolean} `true` if the value equals the nested object property,
   *         `false` otherwise.
   * @example
   *
   *      const user1 = { address: { zipCode: 90210 } };
   *      const user2 = { address: { zipCode: 55555 } };
   *      const user3 = { name: 'Bob' };
   *      const users = [ user1, user2, user3 ];
   *      const isFamous = R.pathEq(['address', 'zipCode'], 90210);
   *      R.filter(isFamous, users); //=> [ user1 ]
   */
  var pathEq = _curry3(function pathEq(_path, val, obj) {
    return equals(path(_path, obj), val);
  });

  /**
   * If the given, non-null object has a value at the given path, returns the
   * value at that path. Otherwise returns the provided default value.
   *
   * @func
   * @memberOf R
   * @since v0.18.0
   * @category Object
   * @typedefn Idx = String | Int
   * @sig a -> [Idx] -> {a} -> a
   * @param {*} d The default value.
   * @param {Array} p The path to use.
   * @param {Object} obj The object to retrieve the nested property from.
   * @return {*} The data at `path` of the supplied object or the default value.
   * @example
   *
   *      R.pathOr('N/A', ['a', 'b'], {a: {b: 2}}); //=> 2
   *      R.pathOr('N/A', ['a', 'b'], {c: {b: 2}}); //=> "N/A"
   */
  var pathOr = _curry3(function pathOr(d, p, obj) {
    return defaultTo(d, path(p, obj));
  });

  /**
   * Returns `true` if the specified object property at given path satisfies the
   * given predicate; `false` otherwise.
   *
   * @func
   * @memberOf R
   * @since v0.19.0
   * @category Logic
   * @typedefn Idx = String | Int
   * @sig (a -> Boolean) -> [Idx] -> {a} -> Boolean
   * @param {Function} pred
   * @param {Array} propPath
   * @param {*} obj
   * @return {Boolean}
   * @see R.propSatisfies, R.path
   * @example
   *
   *      R.pathSatisfies(y => y > 0, ['x', 'y'], {x: {y: 2}}); //=> true
   *      R.pathSatisfies(R.is(Object), [], {x: {y: 2}}); //=> true
   */
  var pathSatisfies = _curry3(function pathSatisfies(pred, propPath, obj) {
    return pred(path(propPath, obj));
  });

  /**
   * Returns a partial copy of an object containing only the keys specified. If
   * the key does not exist, the property is ignored.
   *
   * @func
   * @memberOf R
   * @since v0.1.0
   * @category Object
   * @sig [k] -> {k: v} -> {k: v}
   * @param {Array} names an array of String property names to copy onto a new object
   * @param {Object} obj The object to copy from
   * @return {Object} A new object with only properties from `names` on it.
   * @see R.omit, R.props
   * @example
   *
   *      R.pick(['a', 'd'], {a: 1, b: 2, c: 3, d: 4}); //=> {a: 1, d: 4}
   *      R.pick(['a', 'e', 'f'], {a: 1, b: 2, c: 3, d: 4}); //=> {a: 1}
   */
  var pick = _curry2(function pick(names, obj) {
    var result = {};
    var idx = 0;
    while (idx < names.length) {
      if (names[idx] in obj) {
        result[names[idx]] = obj[names[idx]];
      }
      idx += 1;
    }
    return result;
  });

  /**
   * Similar to `pick` except that this one includes a `key: undefined` pair for
   * properties that don't exist.
   *
   * @func
   * @memberOf R
   * @since v0.1.0
   * @category Object
   * @sig [k] -> {k: v} -> {k: v}
   * @param {Array} names an array of String property names to copy onto a new object
   * @param {Object} obj The object to copy from
   * @return {Object} A new object with only properties from `names` on it.
   * @see R.pick
   * @example
   *
   *      R.pickAll(['a', 'd'], {a: 1, b: 2, c: 3, d: 4}); //=> {a: 1, d: 4}
   *      R.pickAll(['a', 'e', 'f'], {a: 1, b: 2, c: 3, d: 4}); //=> {a: 1, e: undefined, f: undefined}
   */
  var pickAll = _curry2(function pickAll(names, obj) {
    var result = {};
    var idx = 0;
    var len = names.length;
    while (idx < len) {
      var name = names[idx];
      result[name] = obj[name];
      idx += 1;
    }
    return result;
  });

  /**
   * Returns a partial copy of an object containing only the keys that satisfy
   * the supplied predicate.
   *
   * @func
   * @memberOf R
   * @since v0.8.0
   * @category Object
   * @sig ((v, k) -> Boolean) -> {k: v} -> {k: v}
   * @param {Function} pred A predicate to determine whether or not a key
   *        should be included on the output object.
   * @param {Object} obj The object to copy from
   * @return {Object} A new object with only properties that satisfy `pred`
   *         on it.
   * @see R.pick, R.filter
   * @example
   *
   *      const isUpperCase = (val, key) => key.toUpperCase() === key;
   *      R.pickBy(isUpperCase, {a: 1, b: 2, A: 3, B: 4}); //=> {A: 3, B: 4}
   */
  var pickBy = _curry2(function pickBy(test, obj) {
    var result = {};
    for (var prop in obj) {
      if (test(obj[prop], prop, obj)) {
        result[prop] = obj[prop];
      }
    }
    return result;
  });

  /**
   * Returns the left-to-right Kleisli composition of the provided functions,
   * each of which must return a value of a type supported by [`chain`](#chain).
   *
   * `R.pipeK(f, g, h)` is equivalent to `R.pipe(f, R.chain(g), R.chain(h))`.
   *
   * @func
   * @memberOf R
   * @since v0.16.0
   * @category Function
   * @sig Chain m => ((a -> m b), (b -> m c), ..., (y -> m z)) -> (a -> m z)
   * @param {...Function}
   * @return {Function}
   * @see R.composeK
   * @deprecated since v0.26.0
   * @example
   *
   *      //  parseJson :: String -> Maybe *
   *      //  get :: String -> Object -> Maybe *
   *
   *      //  getStateCode :: Maybe String -> Maybe String
   *      const getStateCode = R.pipeK(
   *        parseJson,
   *        get('user'),
   *        get('address'),
   *        get('state'),
   *        R.compose(Maybe.of, R.toUpper)
   *      );
   *
   *      getStateCode('{"user":{"address":{"state":"ny"}}}');
   *      //=> Just('NY')
   *      getStateCode('[Invalid JSON]');
   *      //=> Nothing()
   * @symb R.pipeK(f, g, h)(a) = R.chain(h, R.chain(g, f(a)))
   */
  function pipeK() {
    if (arguments.length === 0) {
      throw new Error('pipeK requires at least one argument');
    }
    return composeK.apply(this, reverse(arguments));
  }

  /**
   * Returns a new list with the given element at the front, followed by the
   * contents of the list.
   *
   * @func
   * @memberOf R
   * @since v0.1.0
   * @category List
   * @sig a -> [a] -> [a]
   * @param {*} el The item to add to the head of the output list.
   * @param {Array} list The array to add to the tail of the output list.
   * @return {Array} A new array.
   * @see R.append
   * @example
   *
   *      R.prepend('fee', ['fi', 'fo', 'fum']); //=> ['fee', 'fi', 'fo', 'fum']
   */
  var prepend = _curry2(function prepend(el, list) {
    return _concat([el], list);
  });

  /**
   * Multiplies together all the elements of a list.
   *
   * @func
   * @memberOf R
   * @since v0.1.0
   * @category Math
   * @sig [Number] -> Number
   * @param {Array} list An array of numbers
   * @return {Number} The product of all the numbers in the list.
   * @see R.reduce
   * @example
   *
   *      R.product([2,4,6,8,100,1]); //=> 38400
   */
  var product = reduce(multiply, 1);

  /**
   * Accepts a function `fn` and a list of transformer functions and returns a
   * new curried function. When the new function is invoked, it calls the
   * function `fn` with parameters consisting of the result of calling each
   * supplied handler on successive arguments to the new function.
   *
   * If more arguments are passed to the returned function than transformer
   * functions, those arguments are passed directly to `fn` as additional
   * parameters. If you expect additional arguments that don't need to be
   * transformed, although you can ignore them, it's best to pass an identity
   * function so that the new function reports the correct arity.
   *
   * @func
   * @memberOf R
   * @since v0.1.0
   * @category Function
   * @sig ((x1, x2, ...) -> z) -> [(a -> x1), (b -> x2), ...] -> (a -> b -> ... -> z)
   * @param {Function} fn The function to wrap.
   * @param {Array} transformers A list of transformer functions
   * @return {Function} The wrapped function.
   * @see R.converge
   * @example
   *
   *      R.useWith(Math.pow, [R.identity, R.identity])(3, 4); //=> 81
   *      R.useWith(Math.pow, [R.identity, R.identity])(3)(4); //=> 81
   *      R.useWith(Math.pow, [R.dec, R.inc])(3, 4); //=> 32
   *      R.useWith(Math.pow, [R.dec, R.inc])(3)(4); //=> 32
   * @symb R.useWith(f, [g, h])(a, b) = f(g(a), h(b))
   */
  var useWith = _curry2(function useWith(fn, transformers) {
    return curryN(transformers.length, function() {
      var args = [];
      var idx = 0;
      while (idx < transformers.length) {
        args.push(transformers[idx].call(this, arguments[idx]));
        idx += 1;
      }
      return fn.apply(this, args.concat(Array.prototype.slice.call(arguments, transformers.length)));
    });
  });

  /**
   * Reasonable analog to SQL `select` statement.
   *
   * @func
   * @memberOf R
   * @since v0.1.0
   * @category Object
   * @category Relation
   * @sig [k] -> [{k: v}] -> [{k: v}]
   * @param {Array} props The property names to project
   * @param {Array} objs The objects to query
   * @return {Array} An array of objects with just the `props` properties.
   * @example
   *
   *      const abby = {name: 'Abby', age: 7, hair: 'blond', grade: 2};
   *      const fred = {name: 'Fred', age: 12, hair: 'brown', grade: 7};
   *      const kids = [abby, fred];
   *      R.project(['name', 'grade'], kids); //=> [{name: 'Abby', grade: 2}, {name: 'Fred', grade: 7}]
   */
  var project = useWith(_map, [pickAll, identity]); // passing `identity` gives correct arity

  /**
   * Returns `true` if the specified object property is equal, in
   * [`R.equals`](#equals) terms, to the given value; `false` otherwise.
   * You can test multiple properties with [`R.whereEq`](#whereEq).
   *
   * @func
   * @memberOf R
   * @since v0.1.0
   * @category Relation
   * @sig String -> a -> Object -> Boolean
   * @param {String} name
   * @param {*} val
   * @param {*} obj
   * @return {Boolean}
   * @see R.whereEq, R.propSatisfies, R.equals
   * @example
   *
   *      const abby = {name: 'Abby', age: 7, hair: 'blond'};
   *      const fred = {name: 'Fred', age: 12, hair: 'brown'};
   *      const rusty = {name: 'Rusty', age: 10, hair: 'brown'};
   *      const alois = {name: 'Alois', age: 15, disposition: 'surly'};
   *      const kids = [abby, fred, rusty, alois];
   *      const hasBrownHair = R.propEq('hair', 'brown');
   *      R.filter(hasBrownHair, kids); //=> [fred, rusty]
   */
  var propEq = _curry3(function propEq(name, val, obj) {
    return equals(val, obj[name]);
  });

  /**
   * Returns `true` if the specified object property is of the given type;
   * `false` otherwise.
   *
   * @func
   * @memberOf R
   * @since v0.16.0
   * @category Type
   * @sig Type -> String -> Object -> Boolean
   * @param {Function} type
   * @param {String} name
   * @param {*} obj
   * @return {Boolean}
   * @see R.is, R.propSatisfies
   * @example
   *
   *      R.propIs(Number, 'x', {x: 1, y: 2});  //=> true
   *      R.propIs(Number, 'x', {x: 'foo'});    //=> false
   *      R.propIs(Number, 'x', {});            //=> false
   */
  var propIs = _curry3(function propIs(type, name, obj) {
    return is(type, obj[name]);
  });

  /**
   * If the given, non-null object has an own property with the specified name,
   * returns the value of that property. Otherwise returns the provided default
   * value.
   *
   * @func
   * @memberOf R
   * @since v0.6.0
   * @category Object
   * @sig a -> String -> Object -> a
   * @param {*} val The default value.
   * @param {String} p The name of the property to return.
   * @param {Object} obj The object to query.
   * @return {*} The value of given property of the supplied object or the default value.
   * @example
   *
   *      const alice = {
   *        name: 'ALICE',
   *        age: 101
   *      };
   *      const favorite = R.prop('favoriteLibrary');
   *      const favoriteWithDefault = R.propOr('Ramda', 'favoriteLibrary');
   *
   *      favorite(alice);  //=> undefined
   *      favoriteWithDefault(alice);  //=> 'Ramda'
   */
  var propOr = _curry3(function propOr(val, p, obj) {
    return pathOr(val, [p], obj);
  });

  /**
   * Returns `true` if the specified object property satisfies the given
   * predicate; `false` otherwise. You can test multiple properties with
   * [`R.where`](#where).
   *
   * @func
   * @memberOf R
   * @since v0.16.0
   * @category Logic
   * @sig (a -> Boolean) -> String -> {String: a} -> Boolean
   * @param {Function} pred
   * @param {String} name
   * @param {*} obj
   * @return {Boolean}
   * @see R.where, R.propEq, R.propIs
   * @example
   *
   *      R.propSatisfies(x => x > 0, 'x', {x: 1, y: 2}); //=> true
   */
  var propSatisfies = _curry3(function propSatisfies(pred, name, obj) {
    return pred(obj[name]);
  });

  /**
   * Acts as multiple `prop`: array of keys in, array of values out. Preserves
   * order.
   *
   * @func
   * @memberOf R
   * @since v0.1.0
   * @category Object
   * @sig [k] -> {k: v} -> [v]
   * @param {Array} ps The property names to fetch
   * @param {Object} obj The object to query
   * @return {Array} The corresponding values or partially applied function.
   * @example
   *
   *      R.props(['x', 'y'], {x: 1, y: 2}); //=> [1, 2]
   *      R.props(['c', 'a', 'b'], {b: 2, a: 1}); //=> [undefined, 1, 2]
   *
   *      const fullName = R.compose(R.join(' '), R.props(['first', 'last']));
   *      fullName({last: 'Bullet-Tooth', age: 33, first: 'Tony'}); //=> 'Tony Bullet-Tooth'
   */
  var props = _curry2(function props(ps, obj) {
    return  ps.map(function(p) {
      return path([p], obj);
    });
  });

  /**
   * Returns a list of numbers from `from` (inclusive) to `to` (exclusive).
   *
   * @func
   * @memberOf R
   * @since v0.1.0
   * @category List
   * @sig Number -> Number -> [Number]
   * @param {Number} from The first number in the list.
   * @param {Number} to One more than the last number in the list.
   * @return {Array} The list of numbers in the set `[a, b)`.
   * @example
   *
   *      R.range(1, 5);    //=> [1, 2, 3, 4]
   *      R.range(50, 53);  //=> [50, 51, 52]
   */
  var range = _curry2(function range(from, to) {
    if (!(_isNumber(from) && _isNumber(to))) {
      throw new TypeError('Both arguments to range must be numbers');
    }
    var result = [];
    var n = from;
    while (n < to) {
      result.push(n);
      n += 1;
    }
    return result;
  });

  /**
   * Returns a single item by iterating through the list, successively calling
   * the iterator function and passing it an accumulator value and the current
   * value from the array, and then passing the result to the next call.
   *
   * Similar to [`reduce`](#reduce), except moves through the input list from the
   * right to the left.
   *
   * The iterator function receives two values: *(value, acc)*, while the arguments'
   * order of `reduce`'s iterator function is *(acc, value)*.
   *
   * Note: `R.reduceRight` does not skip deleted or unassigned indices (sparse
   * arrays), unlike the native `Array.prototype.reduceRight` method. For more details
   * on this behavior, see:
   * https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/reduceRight#Description
   *
   * @func
   * @memberOf R
   * @since v0.1.0
   * @category List
   * @sig ((a, b) -> b) -> b -> [a] -> b
   * @param {Function} fn The iterator function. Receives two values, the current element from the array
   *        and the accumulator.
   * @param {*} acc The accumulator value.
   * @param {Array} list The list to iterate over.
   * @return {*} The final, accumulated value.
   * @see R.reduce, R.addIndex
   * @example
   *
   *      R.reduceRight(R.subtract, 0, [1, 2, 3, 4]) // => (1 - (2 - (3 - (4 - 0)))) = -2
   *      //    -               -2
   *      //   / \              / \
   *      //  1   -            1   3
   *      //     / \              / \
   *      //    2   -     ==>    2  -1
   *      //       / \              / \
   *      //      3   -            3   4
   *      //         / \              / \
   *      //        4   0            4   0
   *
   * @symb R.reduceRight(f, a, [b, c, d]) = f(b, f(c, f(d, a)))
   */
  var reduceRight = _curry3(function reduceRight(fn, acc, list) {
    var idx = list.length - 1;
    while (idx >= 0) {
      acc = fn(list[idx], acc);
      idx -= 1;
    }
    return acc;
  });

  /**
   * Like [`reduce`](#reduce), `reduceWhile` returns a single item by iterating
   * through the list, successively calling the iterator function. `reduceWhile`
   * also takes a predicate that is evaluated before each step. If the predicate
   * returns `false`, it "short-circuits" the iteration and returns the current
   * value of the accumulator.
   *
   * @func
   * @memberOf R
   * @since v0.22.0
   * @category List
   * @sig ((a, b) -> Boolean) -> ((a, b) -> a) -> a -> [b] -> a
   * @param {Function} pred The predicate. It is passed the accumulator and the
   *        current element.
   * @param {Function} fn The iterator function. Receives two values, the
   *        accumulator and the current element.
   * @param {*} a The accumulator value.
   * @param {Array} list The list to iterate over.
   * @return {*} The final, accumulated value.
   * @see R.reduce, R.reduced
   * @example
   *
   *      const isOdd = (acc, x) => x % 2 === 1;
   *      const xs = [1, 3, 5, 60, 777, 800];
   *      R.reduceWhile(isOdd, R.add, 0, xs); //=> 9
   *
   *      const ys = [2, 4, 6]
   *      R.reduceWhile(isOdd, R.add, 111, ys); //=> 111
   */
  var reduceWhile = _curryN(4, [], function _reduceWhile(pred, fn, a, list) {
    return _reduce(function(acc, x) {
      return pred(acc, x) ? fn(acc, x) : _reduced(acc);
    }, a, list);
  });

  /**
   * Returns a value wrapped to indicate that it is the final value of the reduce
   * and transduce functions. The returned value should be considered a black
   * box: the internal structure is not guaranteed to be stable.
   *
   * Note: this optimization is only available to the below functions:
   * - [`reduce`](#reduce)
   * - [`reduceWhile`](#reduceWhile)
   * - [`transduce`](#transduce)
   *
   * @func
   * @memberOf R
   * @since v0.15.0
   * @category List
   * @sig a -> *
   * @param {*} x The final value of the reduce.
   * @return {*} The wrapped value.
   * @see R.reduce, R.reduceWhile, R.transduce
   * @example
   *
   *     R.reduce(
   *       (acc, item) => item > 3 ? R.reduced(acc) : acc.concat(item),
   *       [],
   *       [1, 2, 3, 4, 5]) // [1, 2, 3]
   */
  var reduced = _curry1(_reduced);

  /**
   * Calls an input function `n` times, returning an array containing the results
   * of those function calls.
   *
   * `fn` is passed one argument: The current value of `n`, which begins at `0`
   * and is gradually incremented to `n - 1`.
   *
   * @func
   * @memberOf R
   * @since v0.2.3
   * @category List
   * @sig (Number -> a) -> Number -> [a]
   * @param {Function} fn The function to invoke. Passed one argument, the current value of `n`.
   * @param {Number} n A value between `0` and `n - 1`. Increments after each function call.
   * @return {Array} An array containing the return values of all calls to `fn`.
   * @see R.repeat
   * @example
   *
   *      R.times(R.identity, 5); //=> [0, 1, 2, 3, 4]
   * @symb R.times(f, 0) = []
   * @symb R.times(f, 1) = [f(0)]
   * @symb R.times(f, 2) = [f(0), f(1)]
   */
  var times = _curry2(function times(fn, n) {
    var len = Number(n);
    var idx = 0;
    var list;

    if (len < 0 || isNaN(len)) {
      throw new RangeError('n must be a non-negative number');
    }
    list = new Array(len);
    while (idx < len) {
      list[idx] = fn(idx);
      idx += 1;
    }
    return list;
  });

  /**
   * Returns a fixed list of size `n` containing a specified identical value.
   *
   * @func
   * @memberOf R
   * @since v0.1.1
   * @category List
   * @sig a -> n -> [a]
   * @param {*} value The value to repeat.
   * @param {Number} n The desired size of the output list.
   * @return {Array} A new array containing `n` `value`s.
   * @see R.times
   * @example
   *
   *      R.repeat('hi', 5); //=> ['hi', 'hi', 'hi', 'hi', 'hi']
   *
   *      const obj = {};
   *      const repeatedObjs = R.repeat(obj, 5); //=> [{}, {}, {}, {}, {}]
   *      repeatedObjs[0] === repeatedObjs[1]; //=> true
   * @symb R.repeat(a, 0) = []
   * @symb R.repeat(a, 1) = [a]
   * @symb R.repeat(a, 2) = [a, a]
   */
  var repeat = _curry2(function repeat(value, n) {
    return times(always(value), n);
  });

  /**
   * Replace a substring or regex match in a string with a replacement.
   *
   * The first two parameters correspond to the parameters of the
   * `String.prototype.replace()` function, so the second parameter can also be a
   * function.
   *
   * @func
   * @memberOf R
   * @since v0.7.0
   * @category String
   * @sig RegExp|String -> String -> String -> String
   * @param {RegExp|String} pattern A regular expression or a substring to match.
   * @param {String} replacement The string to replace the matches with.
   * @param {String} str The String to do the search and replacement in.
   * @return {String} The result.
   * @example
   *
   *      R.replace('foo', 'bar', 'foo foo foo'); //=> 'bar foo foo'
   *      R.replace(/foo/, 'bar', 'foo foo foo'); //=> 'bar foo foo'
   *
   *      // Use the "g" (global) flag to replace all occurrences:
   *      R.replace(/foo/g, 'bar', 'foo foo foo'); //=> 'bar bar bar'
   */
  var replace = _curry3(function replace(regex, replacement, str) {
    return str.replace(regex, replacement);
  });

  /**
   * Scan is similar to [`reduce`](#reduce), but returns a list of successively
   * reduced values from the left
   *
   * @func
   * @memberOf R
   * @since v0.10.0
   * @category List
   * @sig ((a, b) -> a) -> a -> [b] -> [a]
   * @param {Function} fn The iterator function. Receives two values, the accumulator and the
   *        current element from the array
   * @param {*} acc The accumulator value.
   * @param {Array} list The list to iterate over.
   * @return {Array} A list of all intermediately reduced values.
   * @see R.reduce, R.mapAccum
   * @example
   *
   *      const numbers = [1, 2, 3, 4];
   *      const factorials = R.scan(R.multiply, 1, numbers); //=> [1, 1, 2, 6, 24]
   * @symb R.scan(f, a, [b, c]) = [a, f(a, b), f(f(a, b), c)]
   */
  var scan = _curry3(function scan(fn, acc, list) {
    var idx = 0;
    var len = list.length;
    var result = [acc];
    while (idx < len) {
      acc = fn(acc, list[idx]);
      result[idx + 1] = acc;
      idx += 1;
    }
    return result;
  });

  /**
   * Transforms a [Traversable](https://github.com/fantasyland/fantasy-land#traversable)
   * of [Applicative](https://github.com/fantasyland/fantasy-land#applicative) into an
   * Applicative of Traversable.
   *
   * Dispatches to the `sequence` method of the second argument, if present.
   *
   * @func
   * @memberOf R
   * @since v0.19.0
   * @category List
   * @sig (Applicative f, Traversable t) => (a -> f a) -> t (f a) -> f (t a)
   * @param {Function} of
   * @param {*} traversable
   * @return {*}
   * @see R.traverse
   * @example
   *
   *      R.sequence(Maybe.of, [Just(1), Just(2), Just(3)]);   //=> Just([1, 2, 3])
   *      R.sequence(Maybe.of, [Just(1), Just(2), Nothing()]); //=> Nothing()
   *
   *      R.sequence(R.of, Just([1, 2, 3])); //=> [Just(1), Just(2), Just(3)]
   *      R.sequence(R.of, Nothing());       //=> [Nothing()]
   */
  var sequence = _curry2(function sequence(of, traversable) {
    return typeof traversable.sequence === 'function' ?
      traversable.sequence(of) :
      reduceRight(
        function(x, acc) { return ap(map(prepend, x), acc); },
        of([]),
        traversable
      );
  });

  /**
   * Returns the result of "setting" the portion of the given data structure
   * focused by the given lens to the given value.
   *
   * @func
   * @memberOf R
   * @since v0.16.0
   * @category Object
   * @typedefn Lens s a = Functor f => (a -> f a) -> s -> f s
   * @sig Lens s a -> a -> s -> s
   * @param {Lens} lens
   * @param {*} v
   * @param {*} x
   * @return {*}
   * @see R.prop, R.lensIndex, R.lensProp
   * @example
   *
   *      const xLens = R.lensProp('x');
   *
   *      R.set(xLens, 4, {x: 1, y: 2});  //=> {x: 4, y: 2}
   *      R.set(xLens, 8, {x: 1, y: 2});  //=> {x: 8, y: 2}
   */
  var set = _curry3(function set(lens, v, x) {
    return over(lens, always(v), x);
  });

  /**
   * Returns a copy of the list, sorted according to the comparator function,
   * which should accept two values at a time and return a negative number if the
   * first value is smaller, a positive number if it's larger, and zero if they
   * are equal. Please note that this is a **copy** of the list. It does not
   * modify the original.
   *
   * @func
   * @memberOf R
   * @since v0.1.0
   * @category List
   * @sig ((a, a) -> Number) -> [a] -> [a]
   * @param {Function} comparator A sorting function :: a -> b -> Int
   * @param {Array} list The list to sort
   * @return {Array} a new array with its elements sorted by the comparator function.
   * @example
   *
   *      const diff = function(a, b) { return a - b; };
   *      R.sort(diff, [4,2,7,5]); //=> [2, 4, 5, 7]
   */
  var sort = _curry2(function sort(comparator, list) {
    return Array.prototype.slice.call(list, 0).sort(comparator);
  });

  /**
   * Sorts the list according to the supplied function.
   *
   * @func
   * @memberOf R
   * @since v0.1.0
   * @category Relation
   * @sig Ord b => (a -> b) -> [a] -> [a]
   * @param {Function} fn
   * @param {Array} list The list to sort.
   * @return {Array} A new list sorted by the keys generated by `fn`.
   * @example
   *
   *      const sortByFirstItem = R.sortBy(R.prop(0));
   *      const pairs = [[-1, 1], [-2, 2], [-3, 3]];
   *      sortByFirstItem(pairs); //=> [[-3, 3], [-2, 2], [-1, 1]]
   *
   *      const sortByNameCaseInsensitive = R.sortBy(R.compose(R.toLower, R.prop('name')));
   *      const alice = {
   *        name: 'ALICE',
   *        age: 101
   *      };
   *      const bob = {
   *        name: 'Bob',
   *        age: -10
   *      };
   *      const clara = {
   *        name: 'clara',
   *        age: 314.159
   *      };
   *      const people = [clara, bob, alice];
   *      sortByNameCaseInsensitive(people); //=> [alice, bob, clara]
   */
  var sortBy = _curry2(function sortBy(fn, list) {
    return Array.prototype.slice.call(list, 0).sort(function(a, b) {
      var aa = fn(a);
      var bb = fn(b);
      return aa < bb ? -1 : aa > bb ? 1 : 0;
    });
  });

  /**
   * Sorts a list according to a list of comparators.
   *
   * @func
   * @memberOf R
   * @since v0.23.0
   * @category Relation
   * @sig [(a, a) -> Number] -> [a] -> [a]
   * @param {Array} functions A list of comparator functions.
   * @param {Array} list The list to sort.
   * @return {Array} A new list sorted according to the comarator functions.
   * @example
   *
   *      const alice = {
   *        name: 'alice',
   *        age: 40
   *      };
   *      const bob = {
   *        name: 'bob',
   *        age: 30
   *      };
   *      const clara = {
   *        name: 'clara',
   *        age: 40
   *      };
   *      const people = [clara, bob, alice];
   *      const ageNameSort = R.sortWith([
   *        R.descend(R.prop('age')),
   *        R.ascend(R.prop('name'))
   *      ]);
   *      ageNameSort(people); //=> [alice, clara, bob]
   */
  var sortWith = _curry2(function sortWith(fns, list) {
    return Array.prototype.slice.call(list, 0).sort(function(a, b) {
      var result = 0;
      var i = 0;
      while (result === 0 && i < fns.length) {
        result = fns[i](a, b);
        i += 1;
      }
      return result;
    });
  });

  /**
   * Splits a string into an array of strings based on the given
   * separator.
   *
   * @func
   * @memberOf R
   * @since v0.1.0
   * @category String
   * @sig (String | RegExp) -> String -> [String]
   * @param {String|RegExp} sep The pattern.
   * @param {String} str The string to separate into an array.
   * @return {Array} The array of strings from `str` separated by `sep`.
   * @see R.join
   * @example
   *
   *      const pathComponents = R.split('/');
   *      R.tail(pathComponents('/usr/local/bin/node')); //=> ['usr', 'local', 'bin', 'node']
   *
   *      R.split('.', 'a.b.c.xyz.d'); //=> ['a', 'b', 'c', 'xyz', 'd']
   */
  var split = invoker(1, 'split');

  /**
   * Splits a given list or string at a given index.
   *
   * @func
   * @memberOf R
   * @since v0.19.0
   * @category List
   * @sig Number -> [a] -> [[a], [a]]
   * @sig Number -> String -> [String, String]
   * @param {Number} index The index where the array/string is split.
   * @param {Array|String} array The array/string to be split.
   * @return {Array}
   * @example
   *
   *      R.splitAt(1, [1, 2, 3]);          //=> [[1], [2, 3]]
   *      R.splitAt(5, 'hello world');      //=> ['hello', ' world']
   *      R.splitAt(-1, 'foobar');          //=> ['fooba', 'r']
   */
  var splitAt = _curry2(function splitAt(index, array) {
    return [slice(0, index, array), slice(index, length(array), array)];
  });

  /**
   * Splits a collection into slices of the specified length.
   *
   * @func
   * @memberOf R
   * @since v0.16.0
   * @category List
   * @sig Number -> [a] -> [[a]]
   * @sig Number -> String -> [String]
   * @param {Number} n
   * @param {Array} list
   * @return {Array}
   * @example
   *
   *      R.splitEvery(3, [1, 2, 3, 4, 5, 6, 7]); //=> [[1, 2, 3], [4, 5, 6], [7]]
   *      R.splitEvery(3, 'foobarbaz'); //=> ['foo', 'bar', 'baz']
   */
  var splitEvery = _curry2(function splitEvery(n, list) {
    if (n <= 0) {
      throw new Error('First argument to splitEvery must be a positive integer');
    }
    var result = [];
    var idx = 0;
    while (idx < list.length) {
      result.push(slice(idx, idx += n, list));
    }
    return result;
  });

  /**
   * Takes a list and a predicate and returns a pair of lists with the following properties:
   *
   *  - the result of concatenating the two output lists is equivalent to the input list;
   *  - none of the elements of the first output list satisfies the predicate; and
   *  - if the second output list is non-empty, its first element satisfies the predicate.
   *
   * @func
   * @memberOf R
   * @since v0.19.0
   * @category List
   * @sig (a -> Boolean) -> [a] -> [[a], [a]]
   * @param {Function} pred The predicate that determines where the array is split.
   * @param {Array} list The array to be split.
   * @return {Array}
   * @example
   *
   *      R.splitWhen(R.equals(2), [1, 2, 3, 1, 2, 3]);   //=> [[1], [2, 3, 1, 2, 3]]
   */
  var splitWhen = _curry2(function splitWhen(pred, list) {
    var idx = 0;
    var len = list.length;
    var prefix = [];

    while (idx < len && !pred(list[idx])) {
      prefix.push(list[idx]);
      idx += 1;
    }

    return [prefix, Array.prototype.slice.call(list, idx)];
  });

  /**
   * Checks if a list starts with the provided sublist.
   *
   * Similarly, checks if a string starts with the provided substring.
   *
   * @func
   * @memberOf R
   * @since v0.24.0
   * @category List
   * @sig [a] -> [a] -> Boolean
   * @sig String -> String -> Boolean
   * @param {*} prefix
   * @param {*} list
   * @return {Boolean}
   * @see R.endsWith
   * @example
   *
   *      R.startsWith('a', 'abc')                //=> true
   *      R.startsWith('b', 'abc')                //=> false
   *      R.startsWith(['a'], ['a', 'b', 'c'])    //=> true
   *      R.startsWith(['b'], ['a', 'b', 'c'])    //=> false
   */
  var startsWith = _curry2(function(prefix, list) {
    return equals(take(prefix.length, list), prefix);
  });

  /**
   * Subtracts its second argument from its first argument.
   *
   * @func
   * @memberOf R
   * @since v0.1.0
   * @category Math
   * @sig Number -> Number -> Number
   * @param {Number} a The first value.
   * @param {Number} b The second value.
   * @return {Number} The result of `a - b`.
   * @see R.add
   * @example
   *
   *      R.subtract(10, 8); //=> 2
   *
   *      const minus5 = R.subtract(R.__, 5);
   *      minus5(17); //=> 12
   *
   *      const complementaryAngle = R.subtract(90);
   *      complementaryAngle(30); //=> 60
   *      complementaryAngle(72); //=> 18
   */
  var subtract = _curry2(function subtract(a, b) {
    return Number(a) - Number(b);
  });

  /**
   * Finds the set (i.e. no duplicates) of all elements contained in the first or
   * second list, but not both.
   *
   * @func
   * @memberOf R
   * @since v0.19.0
   * @category Relation
   * @sig [*] -> [*] -> [*]
   * @param {Array} list1 The first list.
   * @param {Array} list2 The second list.
   * @return {Array} The elements in `list1` or `list2`, but not both.
   * @see R.symmetricDifferenceWith, R.difference, R.differenceWith
   * @example
   *
   *      R.symmetricDifference([1,2,3,4], [7,6,5,4,3]); //=> [1,2,7,6,5]
   *      R.symmetricDifference([7,6,5,4,3], [1,2,3,4]); //=> [7,6,5,1,2]
   */
  var symmetricDifference = _curry2(function symmetricDifference(list1, list2) {
    return concat(difference(list1, list2), difference(list2, list1));
  });

  /**
   * Finds the set (i.e. no duplicates) of all elements contained in the first or
   * second list, but not both. Duplication is determined according to the value
   * returned by applying the supplied predicate to two list elements.
   *
   * @func
   * @memberOf R
   * @since v0.19.0
   * @category Relation
   * @sig ((a, a) -> Boolean) -> [a] -> [a] -> [a]
   * @param {Function} pred A predicate used to test whether two items are equal.
   * @param {Array} list1 The first list.
   * @param {Array} list2 The second list.
   * @return {Array} The elements in `list1` or `list2`, but not both.
   * @see R.symmetricDifference, R.difference, R.differenceWith
   * @example
   *
   *      const eqA = R.eqBy(R.prop('a'));
   *      const l1 = [{a: 1}, {a: 2}, {a: 3}, {a: 4}];
   *      const l2 = [{a: 3}, {a: 4}, {a: 5}, {a: 6}];
   *      R.symmetricDifferenceWith(eqA, l1, l2); //=> [{a: 1}, {a: 2}, {a: 5}, {a: 6}]
   */
  var symmetricDifferenceWith = _curry3(function symmetricDifferenceWith(pred, list1, list2) {
    return concat(differenceWith(pred, list1, list2), differenceWith(pred, list2, list1));
  });

  /**
   * Returns a new list containing the last `n` elements of a given list, passing
   * each value to the supplied predicate function, and terminating when the
   * predicate function returns `false`. Excludes the element that caused the
   * predicate function to fail. The predicate function is passed one argument:
   * *(value)*.
   *
   * @func
   * @memberOf R
   * @since v0.16.0
   * @category List
   * @sig (a -> Boolean) -> [a] -> [a]
   * @sig (a -> Boolean) -> String -> String
   * @param {Function} fn The function called per iteration.
   * @param {Array} xs The collection to iterate over.
   * @return {Array} A new array.
   * @see R.dropLastWhile, R.addIndex
   * @example
   *
   *      const isNotOne = x => x !== 1;
   *
   *      R.takeLastWhile(isNotOne, [1, 2, 3, 4]); //=> [2, 3, 4]
   *
   *      R.takeLastWhile(x => x !== 'R' , 'Ramda'); //=> 'amda'
   */
  var takeLastWhile = _curry2(function takeLastWhile(fn, xs) {
    var idx = xs.length - 1;
    while (idx >= 0 && fn(xs[idx])) {
      idx -= 1;
    }
    return slice(idx + 1, Infinity, xs);
  });

  function XTakeWhile(f, xf) {
    this.xf = xf;
    this.f = f;
  }
  XTakeWhile.prototype['@@transducer/init'] = _xfBase.init;
  XTakeWhile.prototype['@@transducer/result'] = _xfBase.result;
  XTakeWhile.prototype['@@transducer/step'] = function(result, input) {
    return this.f(input) ? this.xf['@@transducer/step'](result, input) : _reduced(result);
  };

  var _xtakeWhile = _curry2(function _xtakeWhile(f, xf) { return new XTakeWhile(f, xf); });

  /**
   * Returns a new list containing the first `n` elements of a given list,
   * passing each value to the supplied predicate function, and terminating when
   * the predicate function returns `false`. Excludes the element that caused the
   * predicate function to fail. The predicate function is passed one argument:
   * *(value)*.
   *
   * Dispatches to the `takeWhile` method of the second argument, if present.
   *
   * Acts as a transducer if a transformer is given in list position.
   *
   * @func
   * @memberOf R
   * @since v0.1.0
   * @category List
   * @sig (a -> Boolean) -> [a] -> [a]
   * @sig (a -> Boolean) -> String -> String
   * @param {Function} fn The function called per iteration.
   * @param {Array} xs The collection to iterate over.
   * @return {Array} A new array.
   * @see R.dropWhile, R.transduce, R.addIndex
   * @example
   *
   *      const isNotFour = x => x !== 4;
   *
   *      R.takeWhile(isNotFour, [1, 2, 3, 4, 3, 2, 1]); //=> [1, 2, 3]
   *
   *      R.takeWhile(x => x !== 'd' , 'Ramda'); //=> 'Ram'
   */
  var takeWhile = _curry2(_dispatchable(['takeWhile'], _xtakeWhile, function takeWhile(fn, xs) {
    var idx = 0;
    var len = xs.length;
    while (idx < len && fn(xs[idx])) {
      idx += 1;
    }
    return slice(0, idx, xs);
  }));

  function XTap(f, xf) {
    this.xf = xf;
    this.f = f;
  }
  XTap.prototype['@@transducer/init'] = _xfBase.init;
  XTap.prototype['@@transducer/result'] = _xfBase.result;
  XTap.prototype['@@transducer/step'] = function(result, input) {
    this.f(input);
    return this.xf['@@transducer/step'](result, input);
  };

  var _xtap = _curry2(function _xtap(f, xf) { return new XTap(f, xf); });

  /**
   * Runs the given function with the supplied object, then returns the object.
   *
   * Acts as a transducer if a transformer is given as second parameter.
   *
   * @func
   * @memberOf R
   * @since v0.1.0
   * @category Function
   * @sig (a -> *) -> a -> a
   * @param {Function} fn The function to call with `x`. The return value of `fn` will be thrown away.
   * @param {*} x
   * @return {*} `x`.
   * @example
   *
   *      const sayX = x => console.log('x is ' + x);
   *      R.tap(sayX, 100); //=> 100
   *      // logs 'x is 100'
   * @symb R.tap(f, a) = a
   */
  var tap = _curry2(_dispatchable([], _xtap, function tap(fn, x) {
    fn(x);
    return x;
  }));

  function _isRegExp(x) {
    return Object.prototype.toString.call(x) === '[object RegExp]';
  }

  /**
   * Determines whether a given string matches a given regular expression.
   *
   * @func
   * @memberOf R
   * @since v0.12.0
   * @category String
   * @sig RegExp -> String -> Boolean
   * @param {RegExp} pattern
   * @param {String} str
   * @return {Boolean}
   * @see R.match
   * @example
   *
   *      R.test(/^x/, 'xyz'); //=> true
   *      R.test(/^y/, 'xyz'); //=> false
   */
  var test = _curry2(function test(pattern, str) {
    if (!_isRegExp(pattern)) {
      throw new TypeError('‘test’ requires a value of type RegExp as its first argument; received ' + toString$1(pattern));
    }
    return _cloneRegExp(pattern).test(str);
  });

  /**
   * Returns the result of applying the onSuccess function to the value inside
   * a successfully resolved promise. This is useful for working with promises
   * inside function compositions.
   *
   * @func
   * @memberOf R
   * @since v0.27.1
   * @category Function
   * @sig (a -> b) -> (Promise e a) -> (Promise e b)
   * @sig (a -> (Promise e b)) -> (Promise e a) -> (Promise e b)
   * @param {Function} onSuccess The function to apply. Can return a value or a promise of a value.
   * @param {Promise} p
   * @return {Promise} The result of calling `p.then(onSuccess)`
   * @see R.otherwise
   * @example
   *
   *      var makeQuery = (email) => ({ query: { email }});
   *
   *      //getMemberName :: String -> Promise ({firstName, lastName})
   *      var getMemberName = R.pipe(
   *        makeQuery,
   *        fetchMember,
   *        R.andThen(R.pick(['firstName', 'lastName']))
   *      );
   */
  var andThen = _curry2(function andThen(f, p) {
    _assertPromise('andThen', p);

    return p.then(f);
  });

  /**
   * The lower case version of a string.
   *
   * @func
   * @memberOf R
   * @since v0.9.0
   * @category String
   * @sig String -> String
   * @param {String} str The string to lower case.
   * @return {String} The lower case version of `str`.
   * @see R.toUpper
   * @example
   *
   *      R.toLower('XYZ'); //=> 'xyz'
   */
  var toLower = invoker(0, 'toLowerCase');

  /**
   * Converts an object into an array of key, value arrays. Only the object's
   * own properties are used.
   * Note that the order of the output array is not guaranteed to be consistent
   * across different JS platforms.
   *
   * @func
   * @memberOf R
   * @since v0.4.0
   * @category Object
   * @sig {String: *} -> [[String,*]]
   * @param {Object} obj The object to extract from
   * @return {Array} An array of key, value arrays from the object's own properties.
   * @see R.fromPairs
   * @example
   *
   *      R.toPairs({a: 1, b: 2, c: 3}); //=> [['a', 1], ['b', 2], ['c', 3]]
   */
  var toPairs = _curry1(function toPairs(obj) {
    var pairs = [];
    for (var prop in obj) {
      if (_has(prop, obj)) {
        pairs[pairs.length] = [prop, obj[prop]];
      }
    }
    return pairs;
  });

  /**
   * Converts an object into an array of key, value arrays. The object's own
   * properties and prototype properties are used. Note that the order of the
   * output array is not guaranteed to be consistent across different JS
   * platforms.
   *
   * @func
   * @memberOf R
   * @since v0.4.0
   * @category Object
   * @sig {String: *} -> [[String,*]]
   * @param {Object} obj The object to extract from
   * @return {Array} An array of key, value arrays from the object's own
   *         and prototype properties.
   * @example
   *
   *      const F = function() { this.x = 'X'; };
   *      F.prototype.y = 'Y';
   *      const f = new F();
   *      R.toPairsIn(f); //=> [['x','X'], ['y','Y']]
   */
  var toPairsIn = _curry1(function toPairsIn(obj) {
    var pairs = [];
    for (var prop in obj) {
      pairs[pairs.length] = [prop, obj[prop]];
    }
    return pairs;
  });

  /**
   * The upper case version of a string.
   *
   * @func
   * @memberOf R
   * @since v0.9.0
   * @category String
   * @sig String -> String
   * @param {String} str The string to upper case.
   * @return {String} The upper case version of `str`.
   * @see R.toLower
   * @example
   *
   *      R.toUpper('abc'); //=> 'ABC'
   */
  var toUpper = invoker(0, 'toUpperCase');

  /**
   * Initializes a transducer using supplied iterator function. Returns a single
   * item by iterating through the list, successively calling the transformed
   * iterator function and passing it an accumulator value and the current value
   * from the array, and then passing the result to the next call.
   *
   * The iterator function receives two values: *(acc, value)*. It will be
   * wrapped as a transformer to initialize the transducer. A transformer can be
   * passed directly in place of an iterator function. In both cases, iteration
   * may be stopped early with the [`R.reduced`](#reduced) function.
   *
   * A transducer is a function that accepts a transformer and returns a
   * transformer and can be composed directly.
   *
   * A transformer is an an object that provides a 2-arity reducing iterator
   * function, step, 0-arity initial value function, init, and 1-arity result
   * extraction function, result. The step function is used as the iterator
   * function in reduce. The result function is used to convert the final
   * accumulator into the return type and in most cases is
   * [`R.identity`](#identity). The init function can be used to provide an
   * initial accumulator, but is ignored by transduce.
   *
   * The iteration is performed with [`R.reduce`](#reduce) after initializing the transducer.
   *
   * @func
   * @memberOf R
   * @since v0.12.0
   * @category List
   * @sig (c -> c) -> ((a, b) -> a) -> a -> [b] -> a
   * @param {Function} xf The transducer function. Receives a transformer and returns a transformer.
   * @param {Function} fn The iterator function. Receives two values, the accumulator and the
   *        current element from the array. Wrapped as transformer, if necessary, and used to
   *        initialize the transducer
   * @param {*} acc The initial accumulator value.
   * @param {Array} list The list to iterate over.
   * @return {*} The final, accumulated value.
   * @see R.reduce, R.reduced, R.into
   * @example
   *
   *      const numbers = [1, 2, 3, 4];
   *      const transducer = R.compose(R.map(R.add(1)), R.take(2));
   *      R.transduce(transducer, R.flip(R.append), [], numbers); //=> [2, 3]
   *
   *      const isOdd = (x) => x % 2 === 1;
   *      const firstOddTransducer = R.compose(R.filter(isOdd), R.take(1));
   *      R.transduce(firstOddTransducer, R.flip(R.append), [], R.range(0, 100)); //=> [1]
   */
  var transduce = curryN(4, function transduce(xf, fn, acc, list) {
    return _reduce(xf(typeof fn === 'function' ? _xwrap(fn) : fn), acc, list);
  });

  /**
   * Transposes the rows and columns of a 2D list.
   * When passed a list of `n` lists of length `x`,
   * returns a list of `x` lists of length `n`.
   *
   *
   * @func
   * @memberOf R
   * @since v0.19.0
   * @category List
   * @sig [[a]] -> [[a]]
   * @param {Array} list A 2D list
   * @return {Array} A 2D list
   * @example
   *
   *      R.transpose([[1, 'a'], [2, 'b'], [3, 'c']]) //=> [[1, 2, 3], ['a', 'b', 'c']]
   *      R.transpose([[1, 2, 3], ['a', 'b', 'c']]) //=> [[1, 'a'], [2, 'b'], [3, 'c']]
   *
   *      // If some of the rows are shorter than the following rows, their elements are skipped:
   *      R.transpose([[10, 11], [20], [], [30, 31, 32]]) //=> [[10, 20, 30], [11, 31], [32]]
   * @symb R.transpose([[a], [b], [c]]) = [a, b, c]
   * @symb R.transpose([[a, b], [c, d]]) = [[a, c], [b, d]]
   * @symb R.transpose([[a, b], [c]]) = [[a, c], [b]]
   */
  var transpose = _curry1(function transpose(outerlist) {
    var i = 0;
    var result = [];
    while (i < outerlist.length) {
      var innerlist = outerlist[i];
      var j = 0;
      while (j < innerlist.length) {
        if (typeof result[j] === 'undefined') {
          result[j] = [];
        }
        result[j].push(innerlist[j]);
        j += 1;
      }
      i += 1;
    }
    return result;
  });

  /**
   * Maps an [Applicative](https://github.com/fantasyland/fantasy-land#applicative)-returning
   * function over a [Traversable](https://github.com/fantasyland/fantasy-land#traversable),
   * then uses [`sequence`](#sequence) to transform the resulting Traversable of Applicative
   * into an Applicative of Traversable.
   *
   * Dispatches to the `traverse` method of the third argument, if present.
   *
   * @func
   * @memberOf R
   * @since v0.19.0
   * @category List
   * @sig (Applicative f, Traversable t) => (a -> f a) -> (a -> f b) -> t a -> f (t b)
   * @param {Function} of
   * @param {Function} f
   * @param {*} traversable
   * @return {*}
   * @see R.sequence
   * @example
   *
   *      // Returns `Maybe.Nothing` if the given divisor is `0`
   *      const safeDiv = n => d => d === 0 ? Maybe.Nothing() : Maybe.Just(n / d)
   *
   *      R.traverse(Maybe.of, safeDiv(10), [2, 4, 5]); //=> Maybe.Just([5, 2.5, 2])
   *      R.traverse(Maybe.of, safeDiv(10), [2, 0, 5]); //=> Maybe.Nothing
   */
  var traverse = _curry3(function traverse(of, f, traversable) {
    return typeof traversable['fantasy-land/traverse'] === 'function' ?
      traversable['fantasy-land/traverse'](f, of) :
      sequence(of, map(f, traversable));
  });

  var ws = '\x09\x0A\x0B\x0C\x0D\x20\xA0\u1680\u180E\u2000\u2001\u2002\u2003' +
           '\u2004\u2005\u2006\u2007\u2008\u2009\u200A\u202F\u205F\u3000\u2028' +
           '\u2029\uFEFF';
  var zeroWidth = '\u200b';
  var hasProtoTrim = (typeof String.prototype.trim === 'function');
  /**
   * Removes (strips) whitespace from both ends of the string.
   *
   * @func
   * @memberOf R
   * @since v0.6.0
   * @category String
   * @sig String -> String
   * @param {String} str The string to trim.
   * @return {String} Trimmed version of `str`.
   * @example
   *
   *      R.trim('   xyz  '); //=> 'xyz'
   *      R.map(R.trim, R.split(',', 'x, y, z')); //=> ['x', 'y', 'z']
   */
  var trim = !hasProtoTrim || (ws.trim() || !zeroWidth.trim()) ?
    _curry1(function trim(str) {
      var beginRx = new RegExp('^[' + ws + '][' + ws + ']*');
      var endRx = new RegExp('[' + ws + '][' + ws + ']*$');
      return str.replace(beginRx, '').replace(endRx, '');
    }) :
    _curry1(function trim(str) {
      return str.trim();
    });

  /**
   * `tryCatch` takes two functions, a `tryer` and a `catcher`. The returned
   * function evaluates the `tryer`; if it does not throw, it simply returns the
   * result. If the `tryer` *does* throw, the returned function evaluates the
   * `catcher` function and returns its result. Note that for effective
   * composition with this function, both the `tryer` and `catcher` functions
   * must return the same type of results.
   *
   * @func
   * @memberOf R
   * @since v0.20.0
   * @category Function
   * @sig (...x -> a) -> ((e, ...x) -> a) -> (...x -> a)
   * @param {Function} tryer The function that may throw.
   * @param {Function} catcher The function that will be evaluated if `tryer` throws.
   * @return {Function} A new function that will catch exceptions and send then to the catcher.
   * @example
   *
   *      R.tryCatch(R.prop('x'), R.F)({x: true}); //=> true
   *      R.tryCatch(() => { throw 'foo'}, R.always('catched'))('bar') // => 'catched'
   *      R.tryCatch(R.times(R.identity), R.always([]))('s') // => []
   *      R.tryCatch(() => { throw 'this is not a valid value'}, (err, value)=>({error : err,  value }))('bar') // => {'error': 'this is not a valid value', 'value': 'bar'}
   */
  var tryCatch = _curry2(function _tryCatch(tryer, catcher) {
    return _arity(tryer.length, function() {
      try {
        return tryer.apply(this, arguments);
      } catch (e) {
        return catcher.apply(this, _concat([e], arguments));
      }
    });
  });

  /**
   * Takes a function `fn`, which takes a single array argument, and returns a
   * function which:
   *
   *   - takes any number of positional arguments;
   *   - passes these arguments to `fn` as an array; and
   *   - returns the result.
   *
   * In other words, `R.unapply` derives a variadic function from a function which
   * takes an array. `R.unapply` is the inverse of [`R.apply`](#apply).
   *
   * @func
   * @memberOf R
   * @since v0.8.0
   * @category Function
   * @sig ([*...] -> a) -> (*... -> a)
   * @param {Function} fn
   * @return {Function}
   * @see R.apply
   * @example
   *
   *      R.unapply(JSON.stringify)(1, 2, 3); //=> '[1,2,3]'
   * @symb R.unapply(f)(a, b) = f([a, b])
   */
  var unapply = _curry1(function unapply(fn) {
    return function() {
      return fn(Array.prototype.slice.call(arguments, 0));
    };
  });

  /**
   * Wraps a function of any arity (including nullary) in a function that accepts
   * exactly 1 parameter. Any extraneous parameters will not be passed to the
   * supplied function.
   *
   * @func
   * @memberOf R
   * @since v0.2.0
   * @category Function
   * @sig (* -> b) -> (a -> b)
   * @param {Function} fn The function to wrap.
   * @return {Function} A new function wrapping `fn`. The new function is guaranteed to be of
   *         arity 1.
   * @see R.binary, R.nAry
   * @example
   *
   *      const takesTwoArgs = function(a, b) {
   *        return [a, b];
   *      };
   *      takesTwoArgs.length; //=> 2
   *      takesTwoArgs(1, 2); //=> [1, 2]
   *
   *      const takesOneArg = R.unary(takesTwoArgs);
   *      takesOneArg.length; //=> 1
   *      // Only 1 argument is passed to the wrapped function
   *      takesOneArg(1, 2); //=> [1, undefined]
   * @symb R.unary(f)(a, b, c) = f(a)
   */
  var unary = _curry1(function unary(fn) {
    return nAry(1, fn);
  });

  /**
   * Returns a function of arity `n` from a (manually) curried function.
   *
   * @func
   * @memberOf R
   * @since v0.14.0
   * @category Function
   * @sig Number -> (a -> b) -> (a -> c)
   * @param {Number} length The arity for the returned function.
   * @param {Function} fn The function to uncurry.
   * @return {Function} A new function.
   * @see R.curry
   * @example
   *
   *      const addFour = a => b => c => d => a + b + c + d;
   *
   *      const uncurriedAddFour = R.uncurryN(4, addFour);
   *      uncurriedAddFour(1, 2, 3, 4); //=> 10
   */
  var uncurryN = _curry2(function uncurryN(depth, fn) {
    return curryN(depth, function() {
      var currentDepth = 1;
      var value = fn;
      var idx = 0;
      var endIdx;
      while (currentDepth <= depth && typeof value === 'function') {
        endIdx = currentDepth === depth ? arguments.length : idx + value.length;
        value = value.apply(this, Array.prototype.slice.call(arguments, idx, endIdx));
        currentDepth += 1;
        idx = endIdx;
      }
      return value;
    });
  });

  /**
   * Builds a list from a seed value. Accepts an iterator function, which returns
   * either false to stop iteration or an array of length 2 containing the value
   * to add to the resulting list and the seed to be used in the next call to the
   * iterator function.
   *
   * The iterator function receives one argument: *(seed)*.
   *
   * @func
   * @memberOf R
   * @since v0.10.0
   * @category List
   * @sig (a -> [b]) -> * -> [b]
   * @param {Function} fn The iterator function. receives one argument, `seed`, and returns
   *        either false to quit iteration or an array of length two to proceed. The element
   *        at index 0 of this array will be added to the resulting array, and the element
   *        at index 1 will be passed to the next call to `fn`.
   * @param {*} seed The seed value.
   * @return {Array} The final list.
   * @example
   *
   *      const f = n => n > 50 ? false : [-n, n + 10];
   *      R.unfold(f, 10); //=> [-10, -20, -30, -40, -50]
   * @symb R.unfold(f, x) = [f(x)[0], f(f(x)[1])[0], f(f(f(x)[1])[1])[0], ...]
   */
  var unfold = _curry2(function unfold(fn, seed) {
    var pair = fn(seed);
    var result = [];
    while (pair && pair.length) {
      result[result.length] = pair[0];
      pair = fn(pair[1]);
    }
    return result;
  });

  /**
   * Combines two lists into a set (i.e. no duplicates) composed of the elements
   * of each list.
   *
   * @func
   * @memberOf R
   * @since v0.1.0
   * @category Relation
   * @sig [*] -> [*] -> [*]
   * @param {Array} as The first list.
   * @param {Array} bs The second list.
   * @return {Array} The first and second lists concatenated, with
   *         duplicates removed.
   * @example
   *
   *      R.union([1, 2, 3], [2, 3, 4]); //=> [1, 2, 3, 4]
   */
  var union = _curry2(compose(uniq, _concat));

  /**
   * Returns a new list containing only one copy of each element in the original
   * list, based upon the value returned by applying the supplied predicate to
   * two list elements. Prefers the first item if two items compare equal based
   * on the predicate.
   *
   * @func
   * @memberOf R
   * @since v0.2.0
   * @category List
   * @sig ((a, a) -> Boolean) -> [a] -> [a]
   * @param {Function} pred A predicate used to test whether two items are equal.
   * @param {Array} list The array to consider.
   * @return {Array} The list of unique items.
   * @example
   *
   *      const strEq = R.eqBy(String);
   *      R.uniqWith(strEq)([1, '1', 2, 1]); //=> [1, 2]
   *      R.uniqWith(strEq)([{}, {}]);       //=> [{}]
   *      R.uniqWith(strEq)([1, '1', 1]);    //=> [1]
   *      R.uniqWith(strEq)(['1', 1, 1]);    //=> ['1']
   */
  var uniqWith = _curry2(function uniqWith(pred, list) {
    var idx = 0;
    var len = list.length;
    var result = [];
    var item;
    while (idx < len) {
      item = list[idx];
      if (!_includesWith(pred, item, result)) {
        result[result.length] = item;
      }
      idx += 1;
    }
    return result;
  });

  /**
   * Combines two lists into a set (i.e. no duplicates) composed of the elements
   * of each list. Duplication is determined according to the value returned by
   * applying the supplied predicate to two list elements.
   *
   * @func
   * @memberOf R
   * @since v0.1.0
   * @category Relation
   * @sig ((a, a) -> Boolean) -> [*] -> [*] -> [*]
   * @param {Function} pred A predicate used to test whether two items are equal.
   * @param {Array} list1 The first list.
   * @param {Array} list2 The second list.
   * @return {Array} The first and second lists concatenated, with
   *         duplicates removed.
   * @see R.union
   * @example
   *
   *      const l1 = [{a: 1}, {a: 2}];
   *      const l2 = [{a: 1}, {a: 4}];
   *      R.unionWith(R.eqBy(R.prop('a')), l1, l2); //=> [{a: 1}, {a: 2}, {a: 4}]
   */
  var unionWith = _curry3(function unionWith(pred, list1, list2) {
    return uniqWith(pred, _concat(list1, list2));
  });

  /**
   * Tests the final argument by passing it to the given predicate function. If
   * the predicate is not satisfied, the function will return the result of
   * calling the `whenFalseFn` function with the same argument. If the predicate
   * is satisfied, the argument is returned as is.
   *
   * @func
   * @memberOf R
   * @since v0.18.0
   * @category Logic
   * @sig (a -> Boolean) -> (a -> a) -> a -> a
   * @param {Function} pred        A predicate function
   * @param {Function} whenFalseFn A function to invoke when the `pred` evaluates
   *                               to a falsy value.
   * @param {*}        x           An object to test with the `pred` function and
   *                               pass to `whenFalseFn` if necessary.
   * @return {*} Either `x` or the result of applying `x` to `whenFalseFn`.
   * @see R.ifElse, R.when, R.cond
   * @example
   *
   *      let safeInc = R.unless(R.isNil, R.inc);
   *      safeInc(null); //=> null
   *      safeInc(1); //=> 2
   */
  var unless = _curry3(function unless(pred, whenFalseFn, x) {
    return pred(x) ? x : whenFalseFn(x);
  });

  /**
   * Shorthand for `R.chain(R.identity)`, which removes one level of nesting from
   * any [Chain](https://github.com/fantasyland/fantasy-land#chain).
   *
   * @func
   * @memberOf R
   * @since v0.3.0
   * @category List
   * @sig Chain c => c (c a) -> c a
   * @param {*} list
   * @return {*}
   * @see R.flatten, R.chain
   * @example
   *
   *      R.unnest([1, [2], [[3]]]); //=> [1, 2, [3]]
   *      R.unnest([[1, 2], [3, 4], [5, 6]]); //=> [1, 2, 3, 4, 5, 6]
   */
  var unnest = chain(_identity);

  /**
   * Takes a predicate, a transformation function, and an initial value,
   * and returns a value of the same type as the initial value.
   * It does so by applying the transformation until the predicate is satisfied,
   * at which point it returns the satisfactory value.
   *
   * @func
   * @memberOf R
   * @since v0.20.0
   * @category Logic
   * @sig (a -> Boolean) -> (a -> a) -> a -> a
   * @param {Function} pred A predicate function
   * @param {Function} fn The iterator function
   * @param {*} init Initial value
   * @return {*} Final value that satisfies predicate
   * @example
   *
   *      R.until(R.gt(R.__, 100), R.multiply(2))(1) // => 128
   */
  var until = _curry3(function until(pred, fn, init) {
    var val = init;
    while (!pred(val)) {
      val = fn(val);
    }
    return val;
  });

  /**
   * Returns a list of all the properties, including prototype properties, of the
   * supplied object.
   * Note that the order of the output array is not guaranteed to be consistent
   * across different JS platforms.
   *
   * @func
   * @memberOf R
   * @since v0.2.0
   * @category Object
   * @sig {k: v} -> [v]
   * @param {Object} obj The object to extract values from
   * @return {Array} An array of the values of the object's own and prototype properties.
   * @see R.values, R.keysIn
   * @example
   *
   *      const F = function() { this.x = 'X'; };
   *      F.prototype.y = 'Y';
   *      const f = new F();
   *      R.valuesIn(f); //=> ['X', 'Y']
   */
  var valuesIn = _curry1(function valuesIn(obj) {
    var prop;
    var vs = [];
    for (prop in obj) {
      vs[vs.length] = obj[prop];
    }
    return vs;
  });

  // `Const` is a functor that effectively ignores the function given to `map`.
  var Const = function(x) {
    return {value: x, 'fantasy-land/map': function() { return this; }};
  };

  /**
   * Returns a "view" of the given data structure, determined by the given lens.
   * The lens's focus determines which portion of the data structure is visible.
   *
   * @func
   * @memberOf R
   * @since v0.16.0
   * @category Object
   * @typedefn Lens s a = Functor f => (a -> f a) -> s -> f s
   * @sig Lens s a -> s -> a
   * @param {Lens} lens
   * @param {*} x
   * @return {*}
   * @see R.prop, R.lensIndex, R.lensProp
   * @example
   *
   *      const xLens = R.lensProp('x');
   *
   *      R.view(xLens, {x: 1, y: 2});  //=> 1
   *      R.view(xLens, {x: 4, y: 2});  //=> 4
   */
  var view = _curry2(function view(lens, x) {
    // Using `Const` effectively ignores the setter function of the `lens`,
    // leaving the value returned by the getter function unmodified.
    return lens(Const)(x).value;
  });

  /**
   * Tests the final argument by passing it to the given predicate function. If
   * the predicate is satisfied, the function will return the result of calling
   * the `whenTrueFn` function with the same argument. If the predicate is not
   * satisfied, the argument is returned as is.
   *
   * @func
   * @memberOf R
   * @since v0.18.0
   * @category Logic
   * @sig (a -> Boolean) -> (a -> a) -> a -> a
   * @param {Function} pred       A predicate function
   * @param {Function} whenTrueFn A function to invoke when the `condition`
   *                              evaluates to a truthy value.
   * @param {*}        x          An object to test with the `pred` function and
   *                              pass to `whenTrueFn` if necessary.
   * @return {*} Either `x` or the result of applying `x` to `whenTrueFn`.
   * @see R.ifElse, R.unless, R.cond
   * @example
   *
   *      // truncate :: String -> String
   *      const truncate = R.when(
   *        R.propSatisfies(R.gt(R.__, 10), 'length'),
   *        R.pipe(R.take(10), R.append('…'), R.join(''))
   *      );
   *      truncate('12345');         //=> '12345'
   *      truncate('0123456789ABC'); //=> '0123456789…'
   */
  var when = _curry3(function when(pred, whenTrueFn, x) {
    return pred(x) ? whenTrueFn(x) : x;
  });

  /**
   * Takes a spec object and a test object; returns true if the test satisfies
   * the spec. Each of the spec's own properties must be a predicate function.
   * Each predicate is applied to the value of the corresponding property of the
   * test object. `where` returns true if all the predicates return true, false
   * otherwise.
   *
   * `where` is well suited to declaratively expressing constraints for other
   * functions such as [`filter`](#filter) and [`find`](#find).
   *
   * @func
   * @memberOf R
   * @since v0.1.1
   * @category Object
   * @sig {String: (* -> Boolean)} -> {String: *} -> Boolean
   * @param {Object} spec
   * @param {Object} testObj
   * @return {Boolean}
   * @see R.propSatisfies, R.whereEq
   * @example
   *
   *      // pred :: Object -> Boolean
   *      const pred = R.where({
   *        a: R.equals('foo'),
   *        b: R.complement(R.equals('bar')),
   *        x: R.gt(R.__, 10),
   *        y: R.lt(R.__, 20)
   *      });
   *
   *      pred({a: 'foo', b: 'xxx', x: 11, y: 19}); //=> true
   *      pred({a: 'xxx', b: 'xxx', x: 11, y: 19}); //=> false
   *      pred({a: 'foo', b: 'bar', x: 11, y: 19}); //=> false
   *      pred({a: 'foo', b: 'xxx', x: 10, y: 19}); //=> false
   *      pred({a: 'foo', b: 'xxx', x: 11, y: 20}); //=> false
   */
  var where = _curry2(function where(spec, testObj) {
    for (var prop in spec) {
      if (_has(prop, spec) && !spec[prop](testObj[prop])) {
        return false;
      }
    }
    return true;
  });

  /**
   * Takes a spec object and a test object; returns true if the test satisfies
   * the spec, false otherwise. An object satisfies the spec if, for each of the
   * spec's own properties, accessing that property of the object gives the same
   * value (in [`R.equals`](#equals) terms) as accessing that property of the
   * spec.
   *
   * `whereEq` is a specialization of [`where`](#where).
   *
   * @func
   * @memberOf R
   * @since v0.14.0
   * @category Object
   * @sig {String: *} -> {String: *} -> Boolean
   * @param {Object} spec
   * @param {Object} testObj
   * @return {Boolean}
   * @see R.propEq, R.where
   * @example
   *
   *      // pred :: Object -> Boolean
   *      const pred = R.whereEq({a: 1, b: 2});
   *
   *      pred({a: 1});              //=> false
   *      pred({a: 1, b: 2});        //=> true
   *      pred({a: 1, b: 2, c: 3});  //=> true
   *      pred({a: 1, b: 1});        //=> false
   */
  var whereEq = _curry2(function whereEq(spec, testObj) {
    return where(map(equals, spec), testObj);
  });

  /**
   * Returns a new list without values in the first argument.
   * [`R.equals`](#equals) is used to determine equality.
   *
   * Acts as a transducer if a transformer is given in list position.
   *
   * @func
   * @memberOf R
   * @since v0.19.0
   * @category List
   * @sig [a] -> [a] -> [a]
   * @param {Array} list1 The values to be removed from `list2`.
   * @param {Array} list2 The array to remove values from.
   * @return {Array} The new array without values in `list1`.
   * @see R.transduce, R.difference, R.remove
   * @example
   *
   *      R.without([1, 2], [1, 2, 1, 3, 4]); //=> [3, 4]
   */
  var without = _curry2(function(xs, list) {
    return reject(flip(_includes)(xs), list);
  });

  /**
   * Exclusive disjunction logical operation.
   * Returns `true` if one of the arguments is truthy and the other is falsy.
   * Otherwise, it returns `false`.
   *
   * @func
   * @memberOf R
   * @since v0.27.1
   * @category Logic
   * @sig a -> b -> Boolean
   * @param {Any} a
   * @param {Any} b
   * @return {Boolean} true if one of the arguments is truthy and the other is falsy
   * @see R.or, R.and
   * @example
   *
   *      R.xor(true, true); //=> false
   *      R.xor(true, false); //=> true
   *      R.xor(false, true); //=> true
   *      R.xor(false, false); //=> false
   */
  var xor = _curry2(function xor(a, b) {
    return Boolean(!a ^ !b);
  });

  /**
   * Creates a new list out of the two supplied by creating each possible pair
   * from the lists.
   *
   * @func
   * @memberOf R
   * @since v0.1.0
   * @category List
   * @sig [a] -> [b] -> [[a,b]]
   * @param {Array} as The first list.
   * @param {Array} bs The second list.
   * @return {Array} The list made by combining each possible pair from
   *         `as` and `bs` into pairs (`[a, b]`).
   * @example
   *
   *      R.xprod([1, 2], ['a', 'b']); //=> [[1, 'a'], [1, 'b'], [2, 'a'], [2, 'b']]
   * @symb R.xprod([a, b], [c, d]) = [[a, c], [a, d], [b, c], [b, d]]
   */
  var xprod = _curry2(function xprod(a, b) { // = xprodWith(prepend); (takes about 3 times as long...)
    var idx = 0;
    var ilen = a.length;
    var j;
    var jlen = b.length;
    var result = [];
    while (idx < ilen) {
      j = 0;
      while (j < jlen) {
        result[result.length] = [a[idx], b[j]];
        j += 1;
      }
      idx += 1;
    }
    return result;
  });

  /**
   * Creates a new list out of the two supplied by pairing up equally-positioned
   * items from both lists. The returned list is truncated to the length of the
   * shorter of the two input lists.
   * Note: `zip` is equivalent to `zipWith(function(a, b) { return [a, b] })`.
   *
   * @func
   * @memberOf R
   * @since v0.1.0
   * @category List
   * @sig [a] -> [b] -> [[a,b]]
   * @param {Array} list1 The first array to consider.
   * @param {Array} list2 The second array to consider.
   * @return {Array} The list made by pairing up same-indexed elements of `list1` and `list2`.
   * @example
   *
   *      R.zip([1, 2, 3], ['a', 'b', 'c']); //=> [[1, 'a'], [2, 'b'], [3, 'c']]
   * @symb R.zip([a, b, c], [d, e, f]) = [[a, d], [b, e], [c, f]]
   */
  var zip = _curry2(function zip(a, b) {
    var rv = [];
    var idx = 0;
    var len = Math.min(a.length, b.length);
    while (idx < len) {
      rv[idx] = [a[idx], b[idx]];
      idx += 1;
    }
    return rv;
  });

  /**
   * Creates a new object out of a list of keys and a list of values.
   * Key/value pairing is truncated to the length of the shorter of the two lists.
   * Note: `zipObj` is equivalent to `pipe(zip, fromPairs)`.
   *
   * @func
   * @memberOf R
   * @since v0.3.0
   * @category List
   * @sig [String] -> [*] -> {String: *}
   * @param {Array} keys The array that will be properties on the output object.
   * @param {Array} values The list of values on the output object.
   * @return {Object} The object made by pairing up same-indexed elements of `keys` and `values`.
   * @example
   *
   *      R.zipObj(['a', 'b', 'c'], [1, 2, 3]); //=> {a: 1, b: 2, c: 3}
   */
  var zipObj = _curry2(function zipObj(keys, values) {
    var idx = 0;
    var len = Math.min(keys.length, values.length);
    var out = {};
    while (idx < len) {
      out[keys[idx]] = values[idx];
      idx += 1;
    }
    return out;
  });

  /**
   * Creates a new list out of the two supplied by applying the function to each
   * equally-positioned pair in the lists. The returned list is truncated to the
   * length of the shorter of the two input lists.
   *
   * @function
   * @memberOf R
   * @since v0.1.0
   * @category List
   * @sig ((a, b) -> c) -> [a] -> [b] -> [c]
   * @param {Function} fn The function used to combine the two elements into one value.
   * @param {Array} list1 The first array to consider.
   * @param {Array} list2 The second array to consider.
   * @return {Array} The list made by combining same-indexed elements of `list1` and `list2`
   *         using `fn`.
   * @example
   *
   *      const f = (x, y) => {
   *        // ...
   *      };
   *      R.zipWith(f, [1, 2, 3], ['a', 'b', 'c']);
   *      //=> [f(1, 'a'), f(2, 'b'), f(3, 'c')]
   * @symb R.zipWith(fn, [a, b, c], [d, e, f]) = [fn(a, d), fn(b, e), fn(c, f)]
   */
  var zipWith = _curry3(function zipWith(fn, a, b) {
    var rv = [];
    var idx = 0;
    var len = Math.min(a.length, b.length);
    while (idx < len) {
      rv[idx] = fn(a[idx], b[idx]);
      idx += 1;
    }
    return rv;
  });

  /**
   * Creates a thunk out of a function. A thunk delays a calculation until
   * its result is needed, providing lazy evaluation of arguments.
   *
   * @func
   * @memberOf R
   * @since v0.26.0
   * @category Function
   * @sig ((a, b, ..., j) -> k) -> (a, b, ..., j) -> (() -> k)
   * @param {Function} fn A function to wrap in a thunk
   * @return {Function} Expects arguments for `fn` and returns a new function
   *  that, when called, applies those arguments to `fn`.
   * @see R.partial, R.partialRight
   * @example
   *
   *      R.thunkify(R.identity)(42)(); //=> 42
   *      R.thunkify((a, b) => a + b)(25, 17)(); //=> 42
   */
  var thunkify = _curry1(function thunkify(fn) {
    return curryN(fn.length, function createThunk() {
      var fnArgs = arguments;
      return function invokeThunk() {
        return fn.apply(this, fnArgs);
      };
    });
  });

  exports.F = F;
  exports.T = T;
  exports.__ = __;
  exports.add = add;
  exports.addIndex = addIndex;
  exports.adjust = adjust;
  exports.all = all;
  exports.allPass = allPass;
  exports.always = always;
  exports.and = and;
  exports.any = any;
  exports.anyPass = anyPass;
  exports.ap = ap;
  exports.aperture = aperture;
  exports.append = append;
  exports.apply = apply;
  exports.applySpec = applySpec;
  exports.applyTo = applyTo;
  exports.ascend = ascend;
  exports.assoc = assoc;
  exports.assocPath = assocPath;
  exports.binary = binary;
  exports.bind = bind;
  exports.both = both;
  exports.call = call;
  exports.chain = chain;
  exports.clamp = clamp;
  exports.clone = clone;
  exports.comparator = comparator;
  exports.complement = complement;
  exports.compose = compose;
  exports.composeK = composeK;
  exports.composeP = composeP;
  exports.composeWith = composeWith;
  exports.concat = concat;
  exports.cond = cond;
  exports.construct = construct;
  exports.constructN = constructN;
  exports.contains = contains$1;
  exports.converge = converge;
  exports.countBy = countBy;
  exports.curry = curry;
  exports.curryN = curryN;
  exports.dec = dec;
  exports.defaultTo = defaultTo;
  exports.descend = descend;
  exports.difference = difference;
  exports.differenceWith = differenceWith;
  exports.dissoc = dissoc;
  exports.dissocPath = dissocPath;
  exports.divide = divide;
  exports.drop = drop;
  exports.dropLast = dropLast$1;
  exports.dropLastWhile = dropLastWhile$1;
  exports.dropRepeats = dropRepeats;
  exports.dropRepeatsWith = dropRepeatsWith;
  exports.dropWhile = dropWhile;
  exports.either = either;
  exports.empty = empty;
  exports.endsWith = endsWith;
  exports.eqBy = eqBy;
  exports.eqProps = eqProps;
  exports.equals = equals;
  exports.evolve = evolve;
  exports.filter = filter;
  exports.find = find;
  exports.findIndex = findIndex;
  exports.findLast = findLast;
  exports.findLastIndex = findLastIndex;
  exports.flatten = flatten;
  exports.flip = flip;
  exports.forEach = forEach;
  exports.forEachObjIndexed = forEachObjIndexed;
  exports.fromPairs = fromPairs;
  exports.groupBy = groupBy;
  exports.groupWith = groupWith;
  exports.gt = gt;
  exports.gte = gte;
  exports.has = has;
  exports.hasIn = hasIn;
  exports.hasPath = hasPath;
  exports.head = head;
  exports.identical = identical;
  exports.identity = identity;
  exports.ifElse = ifElse;
  exports.inc = inc;
  exports.includes = includes;
  exports.indexBy = indexBy;
  exports.indexOf = indexOf;
  exports.init = init;
  exports.innerJoin = innerJoin;
  exports.insert = insert;
  exports.insertAll = insertAll;
  exports.intersection = intersection;
  exports.intersperse = intersperse;
  exports.into = into;
  exports.invert = invert;
  exports.invertObj = invertObj;
  exports.invoker = invoker;
  exports.is = is;
  exports.isEmpty = isEmpty;
  exports.isNil = isNil;
  exports.join = join;
  exports.juxt = juxt;
  exports.keys = keys;
  exports.keysIn = keysIn;
  exports.last = last;
  exports.lastIndexOf = lastIndexOf;
  exports.length = length;
  exports.lens = lens;
  exports.lensIndex = lensIndex;
  exports.lensPath = lensPath;
  exports.lensProp = lensProp;
  exports.lift = lift;
  exports.liftN = liftN;
  exports.lt = lt;
  exports.lte = lte;
  exports.map = map;
  exports.mapAccum = mapAccum;
  exports.mapAccumRight = mapAccumRight;
  exports.mapObjIndexed = mapObjIndexed;
  exports.match = match;
  exports.mathMod = mathMod;
  exports.max = max;
  exports.maxBy = maxBy;
  exports.mean = mean;
  exports.median = median;
  exports.memoizeWith = memoizeWith;
  exports.merge = merge;
  exports.mergeAll = mergeAll;
  exports.mergeDeepLeft = mergeDeepLeft;
  exports.mergeDeepRight = mergeDeepRight;
  exports.mergeDeepWith = mergeDeepWith;
  exports.mergeDeepWithKey = mergeDeepWithKey;
  exports.mergeLeft = mergeLeft;
  exports.mergeRight = mergeRight;
  exports.mergeWith = mergeWith;
  exports.mergeWithKey = mergeWithKey;
  exports.min = min;
  exports.minBy = minBy;
  exports.modulo = modulo;
  exports.move = move;
  exports.multiply = multiply;
  exports.nAry = nAry;
  exports.negate = negate;
  exports.none = none;
  exports.not = not;
  exports.nth = nth;
  exports.nthArg = nthArg;
  exports.o = o;
  exports.objOf = objOf;
  exports.of = of;
  exports.omit = omit;
  exports.once = once;
  exports.or = or;
  exports.otherwise = otherwise;
  exports.over = over;
  exports.pair = pair;
  exports.partial = partial;
  exports.partialRight = partialRight;
  exports.partition = partition;
  exports.path = path;
  exports.paths = paths;
  exports.pathEq = pathEq;
  exports.pathOr = pathOr;
  exports.pathSatisfies = pathSatisfies;
  exports.pick = pick;
  exports.pickAll = pickAll;
  exports.pickBy = pickBy;
  exports.pipe = pipe;
  exports.pipeK = pipeK;
  exports.pipeP = pipeP;
  exports.pipeWith = pipeWith;
  exports.pluck = pluck;
  exports.prepend = prepend;
  exports.product = product;
  exports.project = project;
  exports.prop = prop;
  exports.propEq = propEq;
  exports.propIs = propIs;
  exports.propOr = propOr;
  exports.propSatisfies = propSatisfies;
  exports.props = props;
  exports.range = range;
  exports.reduce = reduce;
  exports.reduceBy = reduceBy;
  exports.reduceRight = reduceRight;
  exports.reduceWhile = reduceWhile;
  exports.reduced = reduced;
  exports.reject = reject;
  exports.remove = remove;
  exports.repeat = repeat;
  exports.replace = replace;
  exports.reverse = reverse;
  exports.scan = scan;
  exports.sequence = sequence;
  exports.set = set;
  exports.slice = slice;
  exports.sort = sort;
  exports.sortBy = sortBy;
  exports.sortWith = sortWith;
  exports.split = split;
  exports.splitAt = splitAt;
  exports.splitEvery = splitEvery;
  exports.splitWhen = splitWhen;
  exports.startsWith = startsWith;
  exports.subtract = subtract;
  exports.sum = sum;
  exports.symmetricDifference = symmetricDifference;
  exports.symmetricDifferenceWith = symmetricDifferenceWith;
  exports.tail = tail;
  exports.take = take;
  exports.takeLast = takeLast;
  exports.takeLastWhile = takeLastWhile;
  exports.takeWhile = takeWhile;
  exports.tap = tap;
  exports.test = test;
  exports.andThen = andThen;
  exports.times = times;
  exports.toLower = toLower;
  exports.toPairs = toPairs;
  exports.toPairsIn = toPairsIn;
  exports.toString = toString$1;
  exports.toUpper = toUpper;
  exports.transduce = transduce;
  exports.transpose = transpose;
  exports.traverse = traverse;
  exports.trim = trim;
  exports.tryCatch = tryCatch;
  exports.type = type;
  exports.unapply = unapply;
  exports.unary = unary;
  exports.uncurryN = uncurryN;
  exports.unfold = unfold;
  exports.union = union;
  exports.unionWith = unionWith;
  exports.uniq = uniq;
  exports.uniqBy = uniqBy;
  exports.uniqWith = uniqWith;
  exports.unless = unless;
  exports.unnest = unnest;
  exports.until = until;
  exports.update = update;
  exports.useWith = useWith;
  exports.values = values;
  exports.valuesIn = valuesIn;
  exports.view = view;
  exports.when = when;
  exports.where = where;
  exports.whereEq = whereEq;
  exports.without = without;
  exports.xor = xor;
  exports.xprod = xprod;
  exports.zip = zip;
  exports.zipObj = zipObj;
  exports.zipWith = zipWith;
  exports.thunkify = thunkify;

  Object.defineProperty(exports, '__esModule', { value: true });

}));