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seq_monadic: add unsat-core extraction with minimization toggle

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check() now records the dependencies of an unsat subset in m_core, exposed via
ptr_vector<u_dependency> const& core(). On l_false it calls minimize_core:
with the new m_min_core flag (set_min_core, default true) it deletion-minimizes
to a minimal unsat subset containing only constraints that participate in the
contradiction; with the flag off it returns all membership dependencies.

Add unit tests asserting the core omits irrelevant constraints (e.g. x in a*,
x in ~a*, y in b* has core {x-constraints} only), exercising both flag states.
The test harness runs with minimization disabled by default.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Copilot-Session: 57b9b87e-950a-49ea-bbb3-ed585646a5a9
This commit is contained in:
Nikolaj Bjorner 2026-07-31 20:53:30 -07:00
parent 1e09b4e6ae
commit 1ba30df028
3 changed files with 141 additions and 4 deletions
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43
src/ast/rewriter/seq_monadic.cpp
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@ -424,10 +424,8 @@ void seq_monadic::add(expr* term, expr* regex, u_dependency* d) {
m_memberships.push_back({ expr_ref(term, m), expr_ref(regex, m), d });
}
lbool seq_monadic::check() {
lbool seq_monadic::decide(vector<std::tuple<expr_ref, expr_ref, u_dependency*>> const& memberships) {
m_model.reset();
vector<std::tuple<expr_ref, expr_ref, u_dependency*>> memberships;
memberships.swap(m_memberships); // consume the asserted memberships
if (memberships.empty())
return l_true; // empty conjunction is vacuously true
m_pin.reset();
@ -463,3 +461,42 @@ lbool seq_monadic::check() {
}
return decide_dnf(combined);
}
void seq_monadic::minimize_core(vector<std::tuple<expr_ref, expr_ref, u_dependency*>> const& memberships) {
m_core.reset();
if (!m_min_core) {
// No minimization: the core is simply every asserted membership's dependency.
for (auto const& [term, regex, d] : memberships)
if (d)
m_core.push_back(d);
return;
}
// Deletion-based minimization: start from the full unsat set and try to drop each
// membership; a membership is kept only if removing it makes the set no longer
// provably unsat. The result is a minimal unsat subset (relevant constraints only).
vector<std::tuple<expr_ref, expr_ref, u_dependency*>> keep(memberships);
unsigned i = 0;
while (i < keep.size()) {
vector<std::tuple<expr_ref, expr_ref, u_dependency*>> trial;
for (unsigned j = 0; j < keep.size(); ++j)
if (j != i)
trial.push_back(keep[j]);
if (decide(trial) == l_false)
keep.swap(trial); // membership i is not needed for unsat
else
++i; // membership i is needed; keep it
}
for (auto const& [term, regex, d] : keep)
if (d)
m_core.push_back(d);
}
lbool seq_monadic::check() {
m_core.reset();
vector<std::tuple<expr_ref, expr_ref, u_dependency*>> memberships;
memberships.swap(m_memberships); // consume the asserted memberships
lbool r = decide(memberships);
if (r == l_false)
minimize_core(memberships);
return r;
}