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Diffstat (limited to 'src/theory/quantifiers/cegqi/nested_qe.cpp')
-rw-r--r-- | src/theory/quantifiers/cegqi/nested_qe.cpp | 148 |
1 files changed, 148 insertions, 0 deletions
diff --git a/src/theory/quantifiers/cegqi/nested_qe.cpp b/src/theory/quantifiers/cegqi/nested_qe.cpp new file mode 100644 index 000000000..7f77a1daf --- /dev/null +++ b/src/theory/quantifiers/cegqi/nested_qe.cpp @@ -0,0 +1,148 @@ +/********************* */ +/*! \file nested_qe.cpp + ** \verbatim + ** Top contributors (to current version): + ** Andrew Reynolds + ** This file is part of the CVC4 project. + ** Copyright (c) 2009-2020 by the authors listed in the file AUTHORS + ** in the top-level source directory and their institutional affiliations. + ** All rights reserved. See the file COPYING in the top-level source + ** directory for licensing information.\endverbatim + ** + ** \brief Methods for counterexample-guided quantifier instantiation + ** based on nested quantifier elimination. + **/ + +#include "theory/quantifiers/cegqi/nested_qe.h" + +#include "expr/node_algorithm.h" +#include "expr/subs.h" +#include "theory/smt_engine_subsolver.h" + +namespace CVC4 { +namespace theory { +namespace quantifiers { + +NestedQe::NestedQe(context::UserContext* u) : d_qnqe(u) {} + +bool NestedQe::process(Node q, std::vector<Node>& lems) +{ + NodeNodeMap::iterator it = d_qnqe.find(q); + if (it != d_qnqe.end()) + { + // already processed + return (*it).second != q; + } + Trace("cegqi-nested-qe") << "Check nested QE on " << q << std::endl; + Node qqe = doNestedQe(q, true); + d_qnqe[q] = qqe; + if (qqe == q) + { + Trace("cegqi-nested-qe") << "...did not apply nested QE" << std::endl; + return false; + } + Trace("cegqi-nested-qe") << "...applied nested QE" << std::endl; + Trace("cegqi-nested-qe") << "Result is " << qqe << std::endl; + + // add as lemma + lems.push_back(q.eqNode(qqe)); + return true; +} + +bool NestedQe::hasProcessed(Node q) const +{ + return d_qnqe.find(q) != d_qnqe.end(); +} + +bool NestedQe::getNestedQuantification( + Node q, std::unordered_set<Node, NodeHashFunction>& nqs) +{ + expr::getKindSubterms(q[1], kind::FORALL, true, nqs); + return !nqs.empty(); +} + +bool NestedQe::hasNestedQuantification(Node q) +{ + std::unordered_set<Node, NodeHashFunction> nqs; + return getNestedQuantification(q, nqs); +} + +Node NestedQe::doNestedQe(Node q, bool keepTopLevel) +{ + Assert(q.getKind() == kind::FORALL); + std::unordered_set<Node, NodeHashFunction> nqs; + if (!getNestedQuantification(q, nqs)) + { + Trace("cegqi-nested-qe-debug") + << "...no nested quantification" << std::endl; + if (keepTopLevel) + { + return q; + } + // just do ordinary quantifier elimination + Node qqe = doQe(q); + Trace("cegqi-nested-qe-debug") << "...did ordinary qe" << std::endl; + return qqe; + } + Trace("cegqi-nested-qe-debug") + << "..." << nqs.size() << " nested quantifiers" << std::endl; + // otherwise, skolemize the arguments of this and apply + std::vector<Node> vars(q[0].begin(), q[0].end()); + Subs sk; + sk.add(vars); + // do nested quantifier elimination on each nested quantifier, skolemizing the + // free variables + Subs snqe; + for (const Node& nq : nqs) + { + Node nqk = sk.apply(nq); + Node nqqe = doNestedQe(nqk); + if (nqqe == nqk) + { + // failed + Trace("cegqi-nested-qe-debug") + << "...failed to apply to nested" << std::endl; + return q; + } + snqe.add(nqk, nqqe); + } + // get the result of nested quantifier elimination + Node qeBody = sk.apply(q[1]); + qeBody = snqe.apply(qeBody); + // undo the skolemization + qeBody = sk.rapply(qeBody, true); + // reconstruct the body + std::vector<Node> qargs; + qargs.push_back(q[0]); + qargs.push_back(qeBody); + if (q.getNumChildren() == 3) + { + qargs.push_back(q[2]); + } + NodeManager* nm = NodeManager::currentNM(); + return nm->mkNode(kind::FORALL, qargs); +} + +Node NestedQe::doQe(Node q) +{ + Assert(q.getKind() == kind::FORALL); + Trace("cegqi-nested-qe") << " Apply qe to " << q << std::endl; + NodeManager* nm = NodeManager::currentNM(); + q = nm->mkNode(kind::EXISTS, q[0], q[1].negate()); + std::unique_ptr<SmtEngine> smt_qe; + initializeSubsolver(smt_qe); + Node qqe = smt_qe->getQuantifierElimination(q, true, false); + if (expr::hasBoundVar(qqe)) + { + Trace("cegqi-nested-qe") << " ...failed QE" << std::endl; + //...failed to apply + return q; + } + Node res = qqe.negate(); + Trace("cegqi-nested-qe") << " ...success, result = " << res << std::endl; + return res; +} + +} // namespace quantifiers +} // namespace theory +} // namespace CVC4 |