pythonfunctionz3z3pyforall

Z3 finds model inconsistent with the axioms


When running this code on Python 3.6.7 with the z3-solver module (4.8.0.0), the model returned by z3 seems not valid with the axioms.

f = z3.Function('f', z3.IntSort(), z3.IntSort(), z3.IntSort())
x = z3.Int('x')
s = z3.Solver()
s.add(f(1, 10) == 42)
s.add(z3.ForAll([x], f(2, x) == f(1, x)))
s.check()
m = s.model()
print(m.eval(f(1, 10)))  # print 0
print(m.eval(f(2, 10)))  # print 0

Why didn't we get 42 as we can expect ? Is there a problem with the axioms or the function ?


Solution

  • Looks like your installation might be busted, as I cannot replicate this:

    $ cat a.py
    import z3
    f = z3.Function('f', z3.IntSort(), z3.IntSort(), z3.IntSort())
    x = z3.Int('x')
    s = z3.Solver()
    s.add(f(1, 10) == 42)
    s.add(z3.ForAll([x], f(2, x) == f(1, x)))
    print s.sexpr()
    s.check()
    m = s.model()
    print(m.eval(f(1, 10)))  # print 0
    print(m.eval(f(2, 10)))  # print 0
    
    $ python a.py
    (declare-fun f (Int Int) Int)
    (assert (= (f 1 10) 42))
    (assert (forall ((x Int)) (= (f 2 x) (f 1 x))))
    
    42
    42
    

    Note that I added print s.sexpr() to your code and it nicely printed the generated SMTLib. Do you see the same?