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/******************************************************************************
* Top contributors (to current version):
* Andrew Reynolds
*
* This file is part of the cvc5 project.
*
* Copyright (c) 2009-2021 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.
* ****************************************************************************
*
* 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 cvc5 {
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>& nqs)
{
expr::getKindSubterms(q[1], kind::FORALL, true, nqs);
return !nqs.empty();
}
bool NestedQe::hasNestedQuantification(Node q)
{
std::unordered_set<Node> nqs;
return getNestedQuantification(q, nqs);
}
Node NestedQe::doNestedQe(Node q, bool keepTopLevel)
{
NodeManager* nm = NodeManager::currentNM();
Node qOrig = q;
bool inputExists = false;
if (q.getKind() == kind::EXISTS)
{
q = nm->mkNode(kind::FORALL, q[0], q[1].negate());
inputExists = true;
}
Assert(q.getKind() == kind::FORALL);
std::unordered_set<Node> nqs;
if (!getNestedQuantification(q, nqs))
{
Trace("cegqi-nested-qe-debug")
<< "...no nested quantification" << std::endl;
if (keepTopLevel)
{
return qOrig;
}
// 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(inputExists ? qeBody.negate() : qeBody);
if (q.getNumChildren() == 3)
{
qargs.push_back(q[2]);
}
return nm->mkNode(inputExists ? kind::EXISTS : 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 cvc5
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