(get-unsat-core) returns empty in Z3

sat-solvers, smt, z3

Solution

You need to add name labels to your assertions so get-unsat-core has labels to use in the unsat core output. Write your assertions like this:

(assert (! one :named a1))
(assert (! two :named a2))
(assert (! three :named a3))
(assert (! four :named a4))
(assert (! five :named a5))
(assert (! six :named a6))
(assert (! secondpartA :named spA))
(assert (! secondpartB :named spB))

and get-unsat-core will print an unsat core.

Documentation for this syntax can be found in the SMTLIB tutorial (PDF file).

Problem

I am using Z3 to extract the unsat-core of an unsatisfiable formula. I am using Z3@Rise interface (web based) to write the following code, ``` (set-logic QF_LIA) (set-option :produce-unsat-cores true) (declare-fun ph1 () Int) (declare-fun ph1p () Int) (declare-fun ph3 () Int) (declare-fun ph3p () Int) (declare-fun ph4 () Int) (declare-fun ph4p () Int) (define-fun one () Bool (= ph3p (+ ph1 1))) (define-fun two () Bool (= ph3 (+ ph1 1))) (define-fun three () Bool (= ph1p (+ ph1 1))) (define-fun four () Bool (= ph4p (+ ph1p 1))) (define-fun five () Bool (>= ph1 0)) (define-fun six () Bool (>= ph4 0)) (define-fun secondpartA () Bool (or (= ph4 0) (<= ph3 ph4) )) (define-fun secondpartB () Bool (or (= ph3p 0) (<= ph4p ph3p) )) (assert one) (assert two) (assert three) (assert four) (assert five) (assert six) (assert secondpartA) (assert secondpartB) (check-sat) (get-unsat-core) ``` check-sat correctly returns 'unsat' but (get-unsat-core) returns empty. Am I missing some configuration/option? Or have I made the example complicated?

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