From 574051df1b79c22848c83225e5be1f28a1028877 Mon Sep 17 00:00:00 2001 From: Federico Mora Date: Tue, 26 Nov 2019 21:13:54 -0800 Subject: [PATCH] Step by step derivation of second int.to.str axiom --- src/smt/theory_str.cpp | 13 ++++++++----- 1 file changed, 8 insertions(+), 5 deletions(-) diff --git a/src/smt/theory_str.cpp b/src/smt/theory_str.cpp index 41701f469..4f81e859d 100644 --- a/src/smt/theory_str.cpp +++ b/src/smt/theory_str.cpp @@ -1881,12 +1881,15 @@ namespace smt { assert_axiom(axiom1); } - // axiom 2: (str.from-int N) should not result in a string with leading zeros. + // axiom 2: The only (str.from-int N) that starts with a "0" is "0". expr_ref zero(mk_string("0"), m); - expr_ref pref(u.str.mk_prefix(zero, ex), m); - // The result does not start with a "0" (~p) xor the result is "0" (q) - // ~p xor q == (p or q) and (~p or ~q) - assert_axiom(m.mk_and(m.mk_or(pref, ctx.mk_eq_atom(ex, zero)), m.mk_or(mk_not(m, pref), mk_not(m, ctx.mk_eq_atom(ex, zero))))); + // let (the result starts with a "0") be p + expr_ref p(u.str.mk_prefix(zero, ex), m); + // let (the result is "0") be q + expr_ref q(ctx.mk_eq_atom(ex, zero), m); + // encoding: the result does NOT start with a "0" (~p) xor the result is "0" (q) + // ~p xor q == (~p or q) and (p or ~q) + assert_axiom(m.mk_and(m.mk_or(mk_not(m, p), q), m.mk_or(p, mk_not(m, q)))); } expr * theory_str::mk_RegexIn(expr * str, expr * regexp) {