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Step by step derivation of second int.to.str axiom

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Federico Mora 2019-11-26 21:13:54 -08:00 • committed by Nikolaj Bjorner
parent 900e707619
commit 574051df1b
1 changed files with 8 additions and 5 deletions
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13
src/smt/theory_str.cpp
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@ -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) {