Unsat core (#91)

cvc5_pythonic_api/cvc5_pythonic.py

@@ -1819,7 +1819,7 @@ def as_string(self):
 
         >>> s = Unit(IntVal(1)) + Unit(IntVal(2))
         >>> s.as_string()
-        '(str.++ (seq.unit 1) (seq.unit 2))'
+        '(seq.++ (seq.unit 1) (seq.unit 2))'
         >>> x = Unit(RealVal(1.5))
         >>> print(x.as_string())
         (seq.unit (/ 3 2))
@@ -6316,14 +6316,40 @@ def statistics(self):
         sat
         >>> stats = s.statistics()
         >>> stats['cvc5::CONSTANT']
-        {'defaulted': True, 'internal': False, 'value': {}}
+        {'default': True, 'internal': False, 'value': {}}
         >>> len(stats.get()) < 10
         True
         >>> len(stats.get(True, True)) > 30
         True
         """
         return self.solver.getStatistics()
 
+    def unsat_core(self):
+        """Return a subset (as a list of Bool expressions) of the assumptions provided to the last check().
+
+        These are the unsat ("failed") assumptions.
+
+        To enable this, set the option "produce-unsat-assumptions" to true.
+
+        >>> a,b,c = Bools('a b c')
+        >>> s = Solver()
+        >>> s.set('produce-unsat-assumptions','true')
+        >>> s.add(Or(a,b),Or(b,c),Not(c))
+        >>> s.check(a,b,c)
+        unsat
+        >>> core = s.unsat_core()
+        >>> a in core
+        False
+        >>> b in core
+        False
+        >>> c in core
+        True
+        >>> s.check(a,b)
+        sat
+        """
+        core = self.solver.getUnsatAssumptions()
+        return [BoolRef(c) for c in core]
+
 
 def SolverFor(logic, ctx=None, logFile=None):
     """Create a solver customized for the given logic.

test/pgm_outputs/unsat_assumptions.py.out

@@ -0,0 +1 @@
+success

test/pgms/unsat_assumptions.py

@@ -0,0 +1,150 @@
+from cvc5_pythonic_api import *
+
+
+def reset_solver(s):
+    s.reset()
+    s.set('produce-unsat-assumptions','true')
+
+def validate_unsat_assumptions(assumptions, core):
+    # checks that the produced unsat assumptions (core) match the assumptions (assumptions) sent to the check function
+    return sum([c in assumptions for c in core]) == len(core) 
+
+
+def check_unsat_assumptions(assertions, core):
+    # This function checks wether, given assertions,  the produced unsat assumptions (core) also lead to unsat result
+    slvr = Solver()
+    slvr.set('produce-unsat-assumptions','true')
+    for a in assertions:
+        slvr.add(a)
+    return s.check(*core) == unsat
+
+
+# To make make sure the unsat_core function works there should be at least one nontrivial solution - a solution that doesn't contain all the assumptions sent in the check function.
+nontrivial_counter = 0  
+
+p1, p2, p3 = Bools('p1 p2 p3')
+x, y = Ints('x y')
+s = Solver()
+reset_solver(s)
+assertions = [Implies(p1, x > 0), Implies(p2, y > x), Implies(p2, y < 1), Implies(p3, y > -3)]
+
+for a in assertions:
+    s.add(a)
+
+assumptions = [p1,p2,p3]
+
+s.check(*assumptions)
+
+core = s.unsat_core()
+
+
+assert validate_unsat_assumptions(assumptions,core)
+assert check_unsat_assumptions(assertions,core)
+if len(core) < len(assumptions):
+    nontrivial_counter += 1
+
+# example 2 - booleans
+
+reset_solver(s)
+
+a, b, c = Bools('a b c')
+
+# Add constraints
+
+assertions = [Or(a, b), Or(Not(a), c), Not(c) ]
+for c in assertions:
+    s.add(c)
+
+
+# Check satisfiability
+assumptions = [a,b,c]
+result = s.check(*assumptions)
+
+unsat_core = s.unsat_core()
+
+assert validate_unsat_assumptions(assumptions,unsat_core) 
+assert check_unsat_assumptions(assertions,assumptions)
+if len(unsat_core) < len(assumptions):
+    nontrivial_counter += 1
+
+# example 3 - booleans
+
+
+reset_solver(s)
+
+a, b, c = Bools('a b c')
+d = Bool('d')
+# Add constraints with boolean operators
+assertions = [And(a, b, Not(c)), Or(a, d), Not(And(a, d)) ]
+for a in assertions:
+    s.add(a)
+
+# Check satisfiability
+assumptions = [a,b,c,d]
+result = s.check(*assumptions)
+
+unsat_core = s.unsat_core()
+
+assert validate_unsat_assumptions(assumptions,unsat_core)
+assert check_unsat_assumptions(assertions,assumptions)
+if len(unsat_core) < len(assumptions):
+    nontrivial_counter += 1
+
+# example 4 - reals
+
+
+
+reset_solver(s)
+
+x = Real('x')
+y = Real('y')
+z = Real('z')
+
+assertions = [x + y == 5, y - z > 2, z > 3 ]
+for a in assertions:
+    s.add(a)
+
+# Check satisfiability
+assumptions = [x > 0, y > 0, z > 0]
+result = s.check(*assumptions)
+
+unsat_core = s.unsat_core()
+
+assert validate_unsat_assumptions(assumptions,unsat_core)
+assert check_unsat_assumptions(assertions,assumptions)
+if len(unsat_core) < len(assumptions):
+    nontrivial_counter += 1
+
+
+# example 5 - strings
+
+
+reset_solver(s)
+
+
+# Define string variables
+s1 = String('s1')
+s2 = String('s2')
+
+# Add string constraints
+assertions = [Or(s1 == "hello", s1 == "world"), s1 + s2 == "helloworld"]
+for a in assertions:
+    s.add(a)
+
+# Check satisfiability
+
+result = s.check( Length(s2) < 2)
+
+unsat_core = s.unsat_core()
+
+assert validate_unsat_assumptions([Length(s2) < 2], unsat_core)
+assert check_unsat_assumptions(assertions,[ Length(s2) < 2 ])
+if len(unsat_core) < len([ Length(s2) < 2 ]):
+    nontrivial_counter += 1
+
+# check that there is at least one nontrivial unsat core
+assert nontrivial_counter >= 1
+
+print('success')
+
+