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z3str3: add auxiliary str.substr axioms (#4617)

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Murphy Berzish 2020-08-06 14:00:50 -05:00 • committed by GitHub
parent 4fa2e23704
commit f4ec63f39c
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src/smt/theory_str.cpp
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@ -1720,6 +1720,31 @@ namespace smt {
rw(case3_rw);
assert_axiom(case3_rw);
}
// Auxiliary axioms
{
// base = "" --> (str.substr base pos len) = ""
{
expr_ref premise(ctx.mk_eq_atom(substrBase, mk_string("")), m);
expr_ref conclusion(ctx.mk_eq_atom(expr, mk_string("")), m);
expr_ref axiom(m.mk_implies(premise, conclusion), m);
assert_axiom_rw(axiom);
}
// len( (str.substr base pos len) ) <= len(base)
{
expr_ref axiom(m_autil.mk_le(mk_strlen(expr), mk_strlen(substrBase)), m);
assert_axiom_rw(axiom);
}
// len >= 0 --> len( (str.substr base pos len) ) <= len
{
expr_ref premise(m_autil.mk_ge(substrLen, mk_int(0)), m);
expr_ref conclusion(m_autil.mk_le(mk_strlen(expr), substrLen), m);
expr_ref axiom(m.mk_implies(premise, conclusion), m);
assert_axiom_rw(axiom);
}
}
}
// (str.replace s t t') is the string obtained by replacing the first occurrence