Z3: eliminate don't care variables

问题

I have a test.smt2 file:

(set-logic QF_IDL)
(declare-const a Int)
(declare-const b Int)
(declare-const c Int)
(assert (or (< a 2) (< b 2 )) )
(check-sat)
(get-model)
(exit)

Is there anyway to tell Z3 to only output a=1 (or b=1)? Because when a is 1, b's value does not matter any more.

I executed z3 smt.relevancy=2 -smt2 test.smt2

(following How do I get Z3 to return minimal model?, although smt.relevancy seems has default value 2), but it still outputs:

sat
(model
  (define-fun b () Int
    2)
  (define-fun a () Int
    1)
)

Thank you!

回答1:

The example given in the answer to the question referred to is slightly out of date. A Solver() will pick a suitable tactic to solve the problem, and it appears that it picks a different one now. We can still get that behavior by using a SimpleSolver() (at a possibly significant performance loss). Here's an updated example:

from z3 import *

x, y = Bools('x y')
s = SimpleSolver()
s.set(auto_config=False,relevancy=2)
s.add(Or(x, y))
print s.check()
print s.model()

Note that the (check-sat) command will not execute the same tactic as the SimpleSolver(); to get the same behavior when solving SMT2 files, we need to use the smt tactic, i.e., use (check-sat-using smt). In many cases it will be beneficial to additionally run the simplifier on the problem first which we can achieve by constructing a custom tactic, e.g., (check-sat-using (then simplify smt))

来源：https://stackoverflow.com/questions/28289410/z3-eliminate-dont-care-variables