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SAT/SMT solving in Haskell | PDF
SAT/SMT solving in

Haskell
Masahiro Sakai (酒井 政裕)

Haskell Day 2016
2016-09-17
Self Introduction

Masahiro Sakai
Twitter: @masahiro_sakai
github: https://github.com/msakai/
G+: https://plus.google.com/+MasahiroSakai
Translated “Software Abstractions”
and TaPL into Japanese with colleagues
Interests: Categorical Programming,
Theorem Proving / Decision Procedures,

…
Agenda
What are SAT and SMT?
Haskell libraries for SMT solving
sbv
toysat/toysmt
Conclusion
What are

SAT and SMT?
What is SAT?
* SAT = Boolean SATisfiability problem
“Is there an assignment that makes given formula true?”
Examples:
(P∨Q)∧(P∨¬Q)∧(¬P∨¬Q) is satisfiable with

{P ↦ True, Q ↦ False}
(P∨Q)∧(P∨¬Q)∧(¬P∨¬Q)∧(¬P∨Q) is unsatisfiable
SAT is NP complete, but state-of-the-art SAT-solver can
often solve problems with millions of variables /
constraints.
What is SMT?
Weakness of SAT: Really low-level representation
Encoding problems into SAT sometimes blows-up
SAT solver cannot leverage high-level knowledge
SMT = Satisfiability Modulo Theories
An approach to overcome the weakness of SAT
Problem Example:

Is there array a, function f, integers i, j such that

“0 ≤ i ∧ i < 10 ∧ (2i+1=j ∨ read(a,i)=0) ∧
f(read(write(a,i,3), j-2)) ≠ f(j-i+1)”?
SMT Solver Impl.

SAT Solver + Theory solvers
SAT solver is responsible for Boolean reasoning
Theory solvers are responsible for handling specific functions/relations etc.
SAT
Solver
Arithmetic
Solver

+, ×, ≤
BitVector
Solver
Uninterpre
ted Function

Solver

f, g, =
Array

Solver

read, write


・・・
Some Applications

of SAT/SMT
Software/Hardware verification
Model checking, Test-case generation, …
Theorem proving
Puzzles: Sudoku, Numberlink, Nonogram, etc.
Type checking in Liquid Haskell
eg: doubles :: [{x : Int | x >= 0}]→[{x : Int | x `mod` 2 = 0}]
Program Synthesis
and more
Haskell libraries for
SMT solving
Some Haskell packages
for SMT
Binding
sbv, smtlib2, simple-smt
z3, bindings-yices, yices-easy, yices-painless
SMT solvers written in Haskell:
toysolver, Smooth
SMT-LIB2 file parser/printer
smt-lib, SmtLib
SMT-LIB2 is a standard

input/output format
for SMT solvers
SBV: SMT Based
Verification in Haskell
SMT library developed by Levent Erkok
It provides:
High-Level DSL for specifying problems in
Haskell, and
Interfaces to multiple SMT solver
backends including Z3, CVC4, Yices,
Boolector.
You can install simply using stack/cabal
“stack install sbv” or “cabal install sbv"
SBV Example: “send more money”

Data.SBV.Examples.Puzzles.SendMoreMoney module
sendMoreMoney :: IO SatResult
sendMoreMoney = sat $ do
ds@[s,e,n,d,m,o,r,y] <- mapM sInteger ["s", "e", "n", "d", "m", "o", "r", "y"]
let isDigit x = x .>= 0 &&& x .<= 9
val xs = sum $ zipWith (*) (reverse xs) (iterate (*10) 1)
send = val [s,e,n,d]
more = val [m,o,r,e]
money = val [m,o,n,e,y]
constrain $ bAll isDigit ds
constrain $ allDifferent ds
constrain $ s ./= 0 &&& m ./= 0
solve [send + more .== money]
SEND

+MORE
————

MONEY
SBV Example: “send more money”

Data.SBV.Examples.Puzzles.SendMoreMoney module
sendMoreMoney :: IO SatResult
sendMoreMoney = sat $ do
ds@[s,e,n,d,m,o,r,y] <- mapM sInteger ["s", "e", "n", "d", "m", "o", "r", "y"]
let isDigit x = x .>= 0 &&& x .<= 9
val xs = sum $ zipWith (*) (reverse xs) (iterate (*10) 1)
send = val [s,e,n,d]
more = val [m,o,r,e]
money = val [m,o,n,e,y]
constrain $ bAll isDigit ds
constrain $ allDifferent ds
constrain $ s ./= 0 &&& m ./= 0
solve [send + more .== money]
SMT problem is defined using Symbolic monad,
and SMT solving is performed by

sat :: Symbolic SBool → IO SatResult
SBV Example: “send more money”

Data.SBV.Examples.Puzzles.SendMoreMoney module
sendMoreMoney :: IO SatResult
sendMoreMoney = sat $ do
ds@[s,e,n,d,m,o,r,y] <- mapM sInteger ["s", "e", "n", "d", "m", "o", "r", "y"]
let isDigit x = x .>= 0 &&& x .<= 9
val xs = sum $ zipWith (*) (reverse xs) (iterate (*10) 1)
send = val [s,e,n,d]
more = val [m,o,r,e]
money = val [m,o,n,e,y]
constrain $ bAll isDigit ds
constrain $ allDifferent ds
constrain $ s ./= 0 &&& m ./= 0
solve [send + more .== money]
sInteger :: String → Symbolic SInteger

creates integer variable
SBV Example: “send more money”

Data.SBV.Examples.Puzzles.SendMoreMoney module
sendMoreMoney :: IO SatResult
sendMoreMoney = sat $ do
ds@[s,e,n,d,m,o,r,y] <- mapM sInteger ["s", "e", "n", "d", "m", "o", "r", "y"]
let isDigit x = x .>= 0 &&& x .<= 9
val xs = sum $ zipWith (*) (reverse xs) (iterate (*10) 1)
send = val [s,e,n,d]
more = val [m,o,r,e]
money = val [m,o,n,e,y]
constrain $ bAll isDigit ds
constrain $ allDifferent ds
constrain $ s ./= 0 &&& m ./= 0
solve [send + more .== money]
Comparison over symbolic values:
we have to use slightly difference operators like (.>=), (&&&).
Because Haskell’s (>=), (&&) returns Bool, but we want SBool.
SBV Example: “send more money”

Data.SBV.Examples.Puzzles.SendMoreMoney module
sendMoreMoney :: IO SatResult
sendMoreMoney = sat $ do
ds@[s,e,n,d,m,o,r,y] <- mapM sInteger ["s", "e", "n", "d", "m", "o", "r", "y"]
let isDigit x = x .>= 0 &&& x .<= 9
val xs = sum $ zipWith (*) (reverse xs) (iterate (*10) 1)
send = val [s,e,n,d]
more = val [m,o,r,e]
money = val [m,o,n,e,y]
constrain $ bAll isDigit ds
constrain $ allDifferent ds
constrain $ s ./= 0 &&& m ./= 0
solve [send + more .== money]
val :: [SInteger] → SInteger is defined as in normal Haskell.
Thanks to the Num type class.
SBV Example: “send more money”

Data.SBV.Examples.Puzzles.SendMoreMoney module
sendMoreMoney :: IO SatResult
sendMoreMoney = sat $ do
ds@[s,e,n,d,m,o,r,y] <- mapM sInteger ["s", "e", "n", "d", "m", "o", "r", "y"]
let isDigit x = x .>= 0 &&& x .<= 9
val xs = sum $ zipWith (*) (reverse xs) (iterate (*10) 1)
send = val [s,e,n,d]
more = val [m,o,r,e]
money = val [m,o,n,e,y]
constrain $ bAll isDigit ds
constrain $ allDifferent ds
constrain $ s ./= 0 &&& m ./= 0
solve [send + more .== money]
Actual constraints specification
SBV Example: “send more money”

Data.SBV.Examples.Puzzles.SendMoreMoney module
sendMoreMoney :: IO SatResult
sendMoreMoney = sat $ do
ds@[s,e,n,d,m,o,r,y] <- mapM sInteger ["s", "e", "n", "d", "m", "o", "r", "y"]
let isDigit x = x .>= 0 &&& x .<= 9
val xs = sum $ zipWith (*) (reverse xs) (iterate (*10) 1)
send = val [s,e,n,d]
more = val [m,o,r,e]
money = val [m,o,n,e,y]
constrain $ bAll isDigit ds
constrain $ allDifferent ds
constrain $ s ./= 0 &&& m ./= 0
solve [send + more .== money]
Satisfiable. Model:
s = 9 :: Integer
e = 5 :: Integer
n = 6 :: Integer
d = 7 :: Integer
m = 1 :: Integer
o = 0 :: Integer
r = 8 :: Integer
y = 2 :: Integer
You need SMT solver Z3

to run the code.
SBV Example: “send more money”

Data.SBV.Examples.Puzzles.SendMoreMoney module
sendMoreMoney :: IO AllSatResult
sendMoreMoney = allSat $ do
ds@[s,e,n,d,m,o,r,y] <- mapM sInteger ["s", "e", "n", "d", "m", "o", "r", "y"]
let isDigit x = x .>= 0 &&& x .<= 9
val xs = sum $ zipWith (*) (reverse xs) (iterate (*10) 1)
send = val [s,e,n,d]
more = val [m,o,r,e]
money = val [m,o,n,e,y]
constrain $ bAll isDigit ds
constrain $ allDifferent ds
constrain $ s ./= 0 &&& m ./= 0
solve [send + more .== money]
By changing sat :: Symbolic SBool → IO SatResult with

allSat :: Symbolic SBool → IO AllSatResult
SBV Summary
This is only one example and sbv includes
variety of examples. You should try!
toysolver package
I’m implementing some decision procedure in Haskell
to leaning the algorithms
https://github.com/msakai/toysolver
http://hackage.haskell.org/package/toysolver
It contains some algorithms/solvers.
In particular, it contains a SAT solver ‘toysat’ and
SMT solver ‘toysmt’
Recalling Last Year …
At Proof Summit 2015,

I talked about how SAT/SMT

solver works.
At that time, I already had implemented SAT
solver ‘toysat’, but not implemented SMT solver
yet.
It triggered my motivation to implement a SMT
solver, I worked hard, and finally I did it!
http://www.slideshare.net/sakai/satsmt
toysat / toysmt
Written in pure Haskell
but implemented in very imperative way
toysat is modestly fast.
It was once the fastest among SAT solvers
written in Haskell. But now mios by Shoji
Narazaki is faster.
toysmt is slow, and has very limited features.
toysmt
toysat based SMT solver
implementation is really native and not-
efficient at all
Theories
Equality and Uninterpreted functions ✓
Linear Real Arithmetic ✓
Bit-vector (currently implementing)
Linear Integer Arithmetic, Array, etc. (not yet)
toysmt: demonstration
(set-option :produce-models true)
(set-logic QF_UFLRA)
(declare-sort U 0)
(declare-fun x () Real)
(declare-fun f (U) Real)
(declare-fun P (U) Bool)
(declare-fun g (U) U)
(declare-fun c () U)
(declare-fun d () U)
(assert (= (P c) (= (g c) c)))
(assert (ite (P c) (> x (f d)) (< x (f d))))
(check-sat)
(get-model)
(exit)
QF_UFLRA.smt2

toysmt: demonstration
$ toysmt QF_UFLRA.smt2

success
…
sat
((define-fun P ((x!1 U)) Bool

(ite (= x!1 (as @3 U)) true false))

(define-fun c () U (as @3 U))

(define-fun d () U (as @4 U))

(define-fun f ((x!1 U)) Real

(ite (= x!1 (as @4 U)) 0 (/ 555555 1)))

(define-fun g ((x!1 U)) U

(ite (= x!1 (as @3 U)) (as @3 U) (as @-1 U)))

(define-fun x () Real (/ 1 10)))
For those who do not
read SEXP
U = {@-1, @1, …, @4, …}
x = 1/10 : Real
c = @3 : U
d = @4 : U
P(x) = if x = @3 then true else false
f(x) = if x = @4 then 0 else 55555
g(x) = if x = @3 then @3 else @-1
toysmt in SMT-COMP 2016
QF_LRA (Main Track)
http://smtcomp.sourceforge.net/2016/results-QF_LRA.shtml?v=1467876482
‘toysmt’ ended up dead last.

But without wrong results! (Thanks to QuickCheck!)
toysmt: Future work
Fill the gap with state-of-the-art solvers (even a little)
There’re lots of rooms for performance improvement.
More theories: Bit-vectors, Integer arithmetic,
Array, …
More features: e.g. Proof-generation
Using ‘toysmt’ as a backend of ‘sbv'.
Re-challenge in next year's SMT-COMP competition.
Conclusion
SAT solvers are amazingly fast for solving many
combinatorial problems
SMT is an extension of SAT to handle high-level
constraints using specialized solvers.
sbv is a neat Haskell library for using SMT
solvers
toysmt is a SMT solver written in Haskell
Further readings
http://www.slideshare.net/sakai/satsmt
http://www.slideshare.net/sakai/
how-a-cdcl-sat-solver-works
Further readings
Handbook of Satisfiability
A. Biere, M. Heule, H. Van
Maaren, and T. Walsh, Eds.
IOS Press, Feb. 2009.
It is a very good book covering
variety of topics related to SAT/
SMT.

SAT/SMT solving in Haskell

  • 1.
    SAT/SMT solving in
 Haskell MasahiroSakai (酒井 政裕)
 Haskell Day 2016 2016-09-17
  • 2.
    Self Introduction
 Masahiro Sakai Twitter:@masahiro_sakai github: https://github.com/msakai/ G+: https://plus.google.com/+MasahiroSakai Translated “Software Abstractions” and TaPL into Japanese with colleagues Interests: Categorical Programming, Theorem Proving / Decision Procedures,
 …
  • 3.
    Agenda What are SATand SMT? Haskell libraries for SMT solving sbv toysat/toysmt Conclusion
  • 4.
  • 5.
    What is SAT? *SAT = Boolean SATisfiability problem “Is there an assignment that makes given formula true?” Examples: (P∨Q)∧(P∨¬Q)∧(¬P∨¬Q) is satisfiable with
 {P ↦ True, Q ↦ False} (P∨Q)∧(P∨¬Q)∧(¬P∨¬Q)∧(¬P∨Q) is unsatisfiable SAT is NP complete, but state-of-the-art SAT-solver can often solve problems with millions of variables / constraints.
  • 6.
    What is SMT? Weaknessof SAT: Really low-level representation Encoding problems into SAT sometimes blows-up SAT solver cannot leverage high-level knowledge SMT = Satisfiability Modulo Theories An approach to overcome the weakness of SAT Problem Example:
 Is there array a, function f, integers i, j such that
 “0 ≤ i ∧ i < 10 ∧ (2i+1=j ∨ read(a,i)=0) ∧ f(read(write(a,i,3), j-2)) ≠ f(j-i+1)”?
  • 7.
    SMT Solver Impl.
 SATSolver + Theory solvers SAT solver is responsible for Boolean reasoning Theory solvers are responsible for handling specific functions/relations etc. SAT Solver Arithmetic Solver
 +, ×, ≤ BitVector Solver Uninterpre ted Function
 Solver
 f, g, = Array
 Solver
 read, write 
 ・・・
  • 8.
    Some Applications
 of SAT/SMT Software/Hardwareverification Model checking, Test-case generation, … Theorem proving Puzzles: Sudoku, Numberlink, Nonogram, etc. Type checking in Liquid Haskell eg: doubles :: [{x : Int | x >= 0}]→[{x : Int | x `mod` 2 = 0}] Program Synthesis and more
  • 9.
  • 10.
    Some Haskell packages forSMT Binding sbv, smtlib2, simple-smt z3, bindings-yices, yices-easy, yices-painless SMT solvers written in Haskell: toysolver, Smooth SMT-LIB2 file parser/printer smt-lib, SmtLib SMT-LIB2 is a standard
 input/output format for SMT solvers
  • 11.
    SBV: SMT Based Verificationin Haskell SMT library developed by Levent Erkok It provides: High-Level DSL for specifying problems in Haskell, and Interfaces to multiple SMT solver backends including Z3, CVC4, Yices, Boolector. You can install simply using stack/cabal “stack install sbv” or “cabal install sbv"
  • 12.
    SBV Example: “sendmore money”
 Data.SBV.Examples.Puzzles.SendMoreMoney module sendMoreMoney :: IO SatResult sendMoreMoney = sat $ do ds@[s,e,n,d,m,o,r,y] <- mapM sInteger ["s", "e", "n", "d", "m", "o", "r", "y"] let isDigit x = x .>= 0 &&& x .<= 9 val xs = sum $ zipWith (*) (reverse xs) (iterate (*10) 1) send = val [s,e,n,d] more = val [m,o,r,e] money = val [m,o,n,e,y] constrain $ bAll isDigit ds constrain $ allDifferent ds constrain $ s ./= 0 &&& m ./= 0 solve [send + more .== money] SEND
 +MORE ————
 MONEY
  • 13.
    SBV Example: “sendmore money”
 Data.SBV.Examples.Puzzles.SendMoreMoney module sendMoreMoney :: IO SatResult sendMoreMoney = sat $ do ds@[s,e,n,d,m,o,r,y] <- mapM sInteger ["s", "e", "n", "d", "m", "o", "r", "y"] let isDigit x = x .>= 0 &&& x .<= 9 val xs = sum $ zipWith (*) (reverse xs) (iterate (*10) 1) send = val [s,e,n,d] more = val [m,o,r,e] money = val [m,o,n,e,y] constrain $ bAll isDigit ds constrain $ allDifferent ds constrain $ s ./= 0 &&& m ./= 0 solve [send + more .== money] SMT problem is defined using Symbolic monad, and SMT solving is performed by
 sat :: Symbolic SBool → IO SatResult
  • 14.
    SBV Example: “sendmore money”
 Data.SBV.Examples.Puzzles.SendMoreMoney module sendMoreMoney :: IO SatResult sendMoreMoney = sat $ do ds@[s,e,n,d,m,o,r,y] <- mapM sInteger ["s", "e", "n", "d", "m", "o", "r", "y"] let isDigit x = x .>= 0 &&& x .<= 9 val xs = sum $ zipWith (*) (reverse xs) (iterate (*10) 1) send = val [s,e,n,d] more = val [m,o,r,e] money = val [m,o,n,e,y] constrain $ bAll isDigit ds constrain $ allDifferent ds constrain $ s ./= 0 &&& m ./= 0 solve [send + more .== money] sInteger :: String → Symbolic SInteger
 creates integer variable
  • 15.
    SBV Example: “sendmore money”
 Data.SBV.Examples.Puzzles.SendMoreMoney module sendMoreMoney :: IO SatResult sendMoreMoney = sat $ do ds@[s,e,n,d,m,o,r,y] <- mapM sInteger ["s", "e", "n", "d", "m", "o", "r", "y"] let isDigit x = x .>= 0 &&& x .<= 9 val xs = sum $ zipWith (*) (reverse xs) (iterate (*10) 1) send = val [s,e,n,d] more = val [m,o,r,e] money = val [m,o,n,e,y] constrain $ bAll isDigit ds constrain $ allDifferent ds constrain $ s ./= 0 &&& m ./= 0 solve [send + more .== money] Comparison over symbolic values: we have to use slightly difference operators like (.>=), (&&&). Because Haskell’s (>=), (&&) returns Bool, but we want SBool.
  • 16.
    SBV Example: “sendmore money”
 Data.SBV.Examples.Puzzles.SendMoreMoney module sendMoreMoney :: IO SatResult sendMoreMoney = sat $ do ds@[s,e,n,d,m,o,r,y] <- mapM sInteger ["s", "e", "n", "d", "m", "o", "r", "y"] let isDigit x = x .>= 0 &&& x .<= 9 val xs = sum $ zipWith (*) (reverse xs) (iterate (*10) 1) send = val [s,e,n,d] more = val [m,o,r,e] money = val [m,o,n,e,y] constrain $ bAll isDigit ds constrain $ allDifferent ds constrain $ s ./= 0 &&& m ./= 0 solve [send + more .== money] val :: [SInteger] → SInteger is defined as in normal Haskell. Thanks to the Num type class.
  • 17.
    SBV Example: “sendmore money”
 Data.SBV.Examples.Puzzles.SendMoreMoney module sendMoreMoney :: IO SatResult sendMoreMoney = sat $ do ds@[s,e,n,d,m,o,r,y] <- mapM sInteger ["s", "e", "n", "d", "m", "o", "r", "y"] let isDigit x = x .>= 0 &&& x .<= 9 val xs = sum $ zipWith (*) (reverse xs) (iterate (*10) 1) send = val [s,e,n,d] more = val [m,o,r,e] money = val [m,o,n,e,y] constrain $ bAll isDigit ds constrain $ allDifferent ds constrain $ s ./= 0 &&& m ./= 0 solve [send + more .== money] Actual constraints specification
  • 18.
    SBV Example: “sendmore money”
 Data.SBV.Examples.Puzzles.SendMoreMoney module sendMoreMoney :: IO SatResult sendMoreMoney = sat $ do ds@[s,e,n,d,m,o,r,y] <- mapM sInteger ["s", "e", "n", "d", "m", "o", "r", "y"] let isDigit x = x .>= 0 &&& x .<= 9 val xs = sum $ zipWith (*) (reverse xs) (iterate (*10) 1) send = val [s,e,n,d] more = val [m,o,r,e] money = val [m,o,n,e,y] constrain $ bAll isDigit ds constrain $ allDifferent ds constrain $ s ./= 0 &&& m ./= 0 solve [send + more .== money] Satisfiable. Model: s = 9 :: Integer e = 5 :: Integer n = 6 :: Integer d = 7 :: Integer m = 1 :: Integer o = 0 :: Integer r = 8 :: Integer y = 2 :: Integer You need SMT solver Z3
 to run the code.
  • 19.
    SBV Example: “sendmore money”
 Data.SBV.Examples.Puzzles.SendMoreMoney module sendMoreMoney :: IO AllSatResult sendMoreMoney = allSat $ do ds@[s,e,n,d,m,o,r,y] <- mapM sInteger ["s", "e", "n", "d", "m", "o", "r", "y"] let isDigit x = x .>= 0 &&& x .<= 9 val xs = sum $ zipWith (*) (reverse xs) (iterate (*10) 1) send = val [s,e,n,d] more = val [m,o,r,e] money = val [m,o,n,e,y] constrain $ bAll isDigit ds constrain $ allDifferent ds constrain $ s ./= 0 &&& m ./= 0 solve [send + more .== money] By changing sat :: Symbolic SBool → IO SatResult with
 allSat :: Symbolic SBool → IO AllSatResult
  • 20.
    SBV Summary This isonly one example and sbv includes variety of examples. You should try!
  • 21.
    toysolver package I’m implementingsome decision procedure in Haskell to leaning the algorithms https://github.com/msakai/toysolver http://hackage.haskell.org/package/toysolver It contains some algorithms/solvers. In particular, it contains a SAT solver ‘toysat’ and SMT solver ‘toysmt’
  • 22.
    Recalling Last Year… At Proof Summit 2015,
 I talked about how SAT/SMT
 solver works. At that time, I already had implemented SAT solver ‘toysat’, but not implemented SMT solver yet. It triggered my motivation to implement a SMT solver, I worked hard, and finally I did it! http://www.slideshare.net/sakai/satsmt
  • 23.
    toysat / toysmt Writtenin pure Haskell but implemented in very imperative way toysat is modestly fast. It was once the fastest among SAT solvers written in Haskell. But now mios by Shoji Narazaki is faster. toysmt is slow, and has very limited features.
  • 24.
    toysmt toysat based SMTsolver implementation is really native and not- efficient at all Theories Equality and Uninterpreted functions ✓ Linear Real Arithmetic ✓ Bit-vector (currently implementing) Linear Integer Arithmetic, Array, etc. (not yet)
  • 25.
    toysmt: demonstration (set-option :produce-modelstrue) (set-logic QF_UFLRA) (declare-sort U 0) (declare-fun x () Real) (declare-fun f (U) Real) (declare-fun P (U) Bool) (declare-fun g (U) U) (declare-fun c () U) (declare-fun d () U) (assert (= (P c) (= (g c) c))) (assert (ite (P c) (> x (f d)) (< x (f d)))) (check-sat) (get-model) (exit) QF_UFLRA.smt2

  • 26.
    toysmt: demonstration $ toysmtQF_UFLRA.smt2
 success … sat ((define-fun P ((x!1 U)) Bool
 (ite (= x!1 (as @3 U)) true false))
 (define-fun c () U (as @3 U))
 (define-fun d () U (as @4 U))
 (define-fun f ((x!1 U)) Real
 (ite (= x!1 (as @4 U)) 0 (/ 555555 1)))
 (define-fun g ((x!1 U)) U
 (ite (= x!1 (as @3 U)) (as @3 U) (as @-1 U)))
 (define-fun x () Real (/ 1 10)))
  • 27.
    For those whodo not read SEXP U = {@-1, @1, …, @4, …} x = 1/10 : Real c = @3 : U d = @4 : U P(x) = if x = @3 then true else false f(x) = if x = @4 then 0 else 55555 g(x) = if x = @3 then @3 else @-1
  • 28.
    toysmt in SMT-COMP2016 QF_LRA (Main Track) http://smtcomp.sourceforge.net/2016/results-QF_LRA.shtml?v=1467876482 ‘toysmt’ ended up dead last.
 But without wrong results! (Thanks to QuickCheck!)
  • 29.
    toysmt: Future work Fillthe gap with state-of-the-art solvers (even a little) There’re lots of rooms for performance improvement. More theories: Bit-vectors, Integer arithmetic, Array, … More features: e.g. Proof-generation Using ‘toysmt’ as a backend of ‘sbv'. Re-challenge in next year's SMT-COMP competition.
  • 30.
    Conclusion SAT solvers areamazingly fast for solving many combinatorial problems SMT is an extension of SAT to handle high-level constraints using specialized solvers. sbv is a neat Haskell library for using SMT solvers toysmt is a SMT solver written in Haskell
  • 31.
  • 32.
    Further readings Handbook ofSatisfiability A. Biere, M. Heule, H. Van Maaren, and T. Walsh, Eds. IOS Press, Feb. 2009. It is a very good book covering variety of topics related to SAT/ SMT.