z3与SMTlib2输入

Question

I just upgraded z3 from 4.1 to 4.3.1, and it seems that the smtlib2 input has changed : now, a function/constant declaration is not deleted by a pop statement.

Here is the SMTlib2 input that works fine with z3 4.1 (and other SMT solvers...), but return with an error with z3 4.3.1 : (error "line 19 column 25: invalid declaration, constant 'bs_2' (whith the given signature) already declared")

(set-option :produce-models true)
(set-option :produce-unsat-cores true)
(set-option :interactive-mode true)
(set-option :print-success false)
(push 1)
(declare-fun bs_1 () Bool)
(push 1)
(declare-fun bs_2 () Bool)
(assert (and  bs_1 (not bs_2)))
(check-sat)
(pop 1)
(push 1)
(declare-fun bs_2 () Bool)
(assert (and  bs_1 (not bs_2)))
(check-sat)
(pop 1)
(pop 1)
(exit)

Removing the last bs_2 declaration works fine with z3 4.3.1, but not for z3 4.1. Am I using the push/pop wrong ?

Answer 1

In Z3 4.3.1, we tried to relax some of the SMT-LIB 2.0 restrictions to make Z3 more convenient to use. For example, we can now write (+ x 2) instead of (+ x 2.0) when x is Real . Declarations are global instead of scoped like in Z3 4.1. The motivation was to allow users to encode problems more succinctly. We can use the following option to enable scoped declarations like in Z3 4.1

(set-option :global-decls false)

That being said, I understand this change is very confusing and counter-intuitive for users that are used to other SMT solvers, or read a manual describing the SMT-LIB standard. Thus, we will change the default back to (set-option :global-decls false) .