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https://github.com/Z3Prover/z3
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A new axiomatization for "stoi"
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CEisenhofer
parent
57692811fa
commit
6fa354102a
2 changed files with 160 additions and 1 deletions
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@ -546,7 +546,7 @@ namespace smt {
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else if (m_seq.str.is_itos(n))
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m_axioms.itos_axiom(n);
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else if (m_seq.str.is_stoi(n))
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m_axioms.stoi_axiom(n);
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add_stoi_nseq_axioms(n);
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else if (m_seq.str.is_lt(n))
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m_axioms.lt_axiom(n);
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else if (m_seq.str.is_le(n))
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@ -655,6 +655,10 @@ namespace smt {
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// there is nothing to do for the string solver, as there are no string constraints
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if (!has_eq_or_mem && m_ho_terms.empty() && !has_unhandled_preds()) {
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if (!check_stoi_coherence()) {
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TRACE(seq, tout << "nseq final_check: stoi coherence added axioms, FC_CONTINUE\n");
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return FC_CONTINUE;
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}
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TRACE(seq, tout << "nseq final_check: empty state+ho, FC_DONE (no solve)\n");
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m_nielsen.reset();
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m_nielsen.create_root();
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@ -680,6 +684,10 @@ namespace smt {
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}
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if (!has_eq_or_mem && !has_unhandled_preds()) {
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if (!check_stoi_coherence()) {
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TRACE(seq, tout << "nseq final_check: stoi coherence added axioms, FC_CONTINUE\n");
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return FC_CONTINUE;
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}
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TRACE(seq, tout << "nseq final_check: empty state (after ho), FC_DONE (no solve)\n");
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m_nielsen.reset();
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m_nielsen.create_root();
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@ -732,6 +740,8 @@ namespace smt {
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m_nielsen.set_sat_node(m_nielsen.root());
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if (!check_length_coherence())
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return FC_CONTINUE;
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if (!check_stoi_coherence())
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return FC_CONTINUE;
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TRACE(seq, tout << "pre-check done\n");
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return FC_DONE;
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default:
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@ -772,6 +782,9 @@ namespace smt {
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if (!check_length_coherence())
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return FC_CONTINUE;
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if (!check_stoi_coherence())
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return FC_CONTINUE;
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CTRACE(seq, !has_unhandled_preds(), display(tout << "done\n"));
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if (!all_sat)
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return FC_CONTINUE;
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@ -1452,6 +1465,143 @@ namespace smt {
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return l_undef; // mixed constraints; let DFS decide
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}
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// -----------------------------------------------------------------------
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// stoi (str.to_int) axiomatization for nseq
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//
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// Basic axioms (added once when the term becomes relevant):
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// stoi(s) >= -1
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// stoi("") = -1
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// stoi(s) >= 0 <=> s ∈ [0-9]+
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//
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// Inductive coherence (added in final_check once the arith solver has
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// committed to a concrete length k for s):
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// stoi_axiom(stoi_e, k) — the position-by-position unfolding from
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// seq_axioms that computes the exact integer value.
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// -----------------------------------------------------------------------
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void theory_nseq::add_stoi_nseq_axioms(expr* stoi_e) {
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expr* s = nullptr;
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VERIFY(m_seq.str.is_stoi(stoi_e, s));
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// stoi(s) >= -1
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{
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expr_ref ge_m1(m_autil.mk_ge(stoi_e, m_autil.mk_int(-1)), m);
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literal lit = mk_literal(ge_m1);
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ctx.mark_as_relevant(lit);
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ctx.mk_th_axiom(get_id(), 1, &lit);
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}
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// stoi("") = -1
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{
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expr_ref empty_s(m_seq.str.mk_empty(s->get_sort()), m);
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expr_ref stoi_empty(m_seq.str.mk_stoi(empty_s), m);
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expr_ref eq_neg1(m.mk_eq(stoi_empty, m_autil.mk_int(-1)), m);
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literal lit = mk_literal(eq_neg1);
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ctx.mark_as_relevant(lit);
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ctx.mk_th_axiom(get_id(), 1, &lit);
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}
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// stoi(s) >= 0 <=> s ∈ [0-9]+
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{
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expr_ref re_digit(m_seq.re.mk_range(m_seq.str.mk_string("0"), m_seq.str.mk_string("9")), m);
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expr_ref re_plus(m_seq.re.mk_plus(re_digit), m);
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expr_ref in_re(m_seq.re.mk_in_re(s, re_plus), m);
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expr_ref ge0(m_autil.mk_ge(stoi_e, m_autil.mk_int(0)), m);
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literal lit_in = mk_literal(in_re);
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literal lit_ge0 = mk_literal(ge0);
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ctx.mark_as_relevant(lit_in);
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ctx.mark_as_relevant(lit_ge0);
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// stoi(s) >= 0 => s ∈ [0-9]+
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{
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literal clause[] = { ~lit_ge0, lit_in };
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ctx.mk_th_axiom(get_id(), 2, clause);
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}
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// s ∈ [0-9]+ => stoi(s) >= 0
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{
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literal clause[] = { ~lit_in, lit_ge0 };
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ctx.mk_th_axiom(get_id(), 2, clause);
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}
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}
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// Track for coherence check
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if (!m_stoi_set.contains(stoi_e)) {
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m_stoi_set.insert(stoi_e);
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ctx.push_trail(insert_obj_trail(m_stoi_set, stoi_e));
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ctx.push_trail(restore_vector(m_stoi_terms));
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m_stoi_terms.push_back(stoi_e);
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}
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}
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// Returns true if no new axioms were needed (FC_DONE is safe to return),
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// false if the inductive stoi axiom was instantiated (caller should FC_CONTINUE).
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bool theory_nseq::check_stoi_coherence() {
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if (m_stoi_terms.empty())
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return true;
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bool progress = false;
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for (expr* stoi_e : m_stoi_terms) {
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expr* s = nullptr;
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VERIFY(m_seq.str.is_stoi(stoi_e, s));
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expr_ref len_expr(m_seq.str.mk_length(s), m);
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rational val;
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if (!m_arith_value.get_value(len_expr, val) || !val.is_unsigned())
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continue;
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unsigned k = val.get_unsigned();
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if (k == 0)
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continue; // empty string: handled by basic axiom stoi("") = -1
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// Only instantiate if we haven't yet done so at this depth
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unsigned prev_k = 0;
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if (m_stoi_depth.contains(stoi_e))
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prev_k = m_stoi_depth[stoi_e];
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if (prev_k >= k)
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continue;
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TRACE(seq, tout << "nseq stoi coherence: instantiating depth " << k
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<< " for " << mk_pp(stoi_e, m) << "\n");
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IF_VERBOSE(1, verbose_stream() << "nseq stoi coherence: instantiating depth "
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<< k << " for " << mk_pp(stoi_e, m) << "\n";);
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// Positional unfolding: stoi(s, i) = 10*stoi(s, i-1) + digit(s[i])
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m_axioms.stoi_axiom(stoi_e, k);
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// Explicit upper bound: len(s)=k && stoi(s) >= 0 => stoi(s) <= 10^k-1
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// (digit2int for symbolic characters has no arith bounds, so the
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// positional unfolding alone does not constrain stoi(s) sufficiently)
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{
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rational max_val(1);
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for (unsigned i = 0; i < k; ++i) {
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max_val *= 10;
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}
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--max_val; // 10^k - 1
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expr_ref le_max(m_autil.mk_le(stoi_e, m_autil.mk_int(max_val)), m);
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expr_ref ge0(m_autil.mk_ge(stoi_e, m_autil.mk_int(0)), m);
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expr_ref len_eq_k(m.mk_eq(len_expr, m_autil.mk_int(k)), m);
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literal lit_ge0 = mk_literal(ge0);
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literal lit_le_max = mk_literal(le_max);
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literal lit_len_eq = mk_literal(len_eq_k);
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ctx.mark_as_relevant(lit_ge0);
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ctx.mark_as_relevant(lit_le_max);
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ctx.mark_as_relevant(lit_len_eq);
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literal clause[] = { ~lit_len_eq, ~lit_ge0, lit_le_max };
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ctx.mk_th_axiom(get_id(), 3, clause);
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}
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m_stoi_depth.insert_if_not_there(stoi_e, 0);
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m_stoi_depth[stoi_e] = k;
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progress = true;
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}
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return !progress;
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}
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bool theory_nseq::check_length_coherence() {
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if (m_relevant_lengths.empty())
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return true;
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@ -83,6 +83,11 @@ namespace smt {
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ptr_vector<app> m_ho_terms;
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unsigned m_num_ho_unfolds = 0;
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// stoi (str.to_int) coherence tracking
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ptr_vector<expr> m_stoi_terms; // stoi terms that need coherence checking
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obj_hashtable<expr> m_stoi_set; // dedup guard for m_stoi_terms
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obj_map<expr, unsigned> m_stoi_depth; // max k for which stoi_axiom(e, k) was called
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// unhandled boolean string predicates (prefixof, suffixof, contains, etc.)
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unsigned m_num_unhandled_bool = 0;
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@ -158,6 +163,10 @@ namespace smt {
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bool check_length_coherence();
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// stoi axiom helpers
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void add_stoi_nseq_axioms(expr* stoi_e);
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bool check_stoi_coherence();
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public:
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theory_nseq(context& ctx);
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};
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