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/****************************************************************************** |
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* Top contributors (to current version): |
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* Andrew Reynolds |
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* |
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* This file is part of the cvc5 project. |
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* |
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* Copyright (c) 2009-2021 by the authors listed in the file AUTHORS |
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* in the top-level source directory and their institutional affiliations. |
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* All rights reserved. See the file COPYING in the top-level source |
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* directory for licensing information. |
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* **************************************************************************** |
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* |
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* The module for managing witness form conversion in proofs. |
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*/ |
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#include "smt/witness_form.h" |
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#include "expr/skolem_manager.h" |
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#include "theory/rewriter.h" |
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namespace cvc5 { |
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namespace smt { |
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WitnessFormGenerator::WitnessFormGenerator(ProofNodeManager* pnm) |
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: d_tcpg(pnm, |
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nullptr, |
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TConvPolicy::FIXPOINT, |
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TConvCachePolicy::NEVER, |
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"WfGenerator::TConvProofGenerator", |
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nullptr, |
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true), |
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d_wintroPf(pnm, nullptr, nullptr, "WfGenerator::LazyCDProof"), |
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d_pskPf(pnm, nullptr, "WfGenerator::PurifySkolemProof") |
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{ |
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} |
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std::shared_ptr<ProofNode> WitnessFormGenerator::getProofFor(Node eq) |
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{ |
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if (eq.getKind() != kind::EQUAL) |
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{ |
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// expecting an equality |
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return nullptr; |
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} |
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Node lhs = eq[0]; |
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Node rhs = convertToWitnessForm(eq[0]); |
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if (rhs != eq[1]) |
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{ |
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// expecting witness form |
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return nullptr; |
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} |
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std::shared_ptr<ProofNode> pn = d_tcpg.getProofFor(eq); |
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Assert(pn != nullptr); |
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return pn; |
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} |
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std::string WitnessFormGenerator::identify() const |
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{ |
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return "WitnessFormGenerator"; |
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} |
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Node WitnessFormGenerator::convertToWitnessForm(Node t) |
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{ |
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Node tw = SkolemManager::getOriginalForm(t); |
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if (t == tw) |
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{ |
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// trivial case |
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return tw; |
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} |
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std::unordered_set<TNode>::iterator it; |
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std::vector<TNode> visit; |
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TNode cur; |
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TNode curw; |
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visit.push_back(t); |
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do |
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{ |
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cur = visit.back(); |
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visit.pop_back(); |
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it = d_visited.find(cur); |
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if (it == d_visited.end()) |
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{ |
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d_visited.insert(cur); |
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curw = SkolemManager::getOriginalForm(cur); |
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// if its witness form is different |
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if (cur != curw) |
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{ |
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if (cur.isVar()) |
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{ |
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Node eq = cur.eqNode(curw); |
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// equality between a variable and its original form |
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d_eqs.insert(eq); |
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// ------- SKOLEM_INTRO |
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// k = t |
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d_wintroPf.addStep(eq, PfRule::SKOLEM_INTRO, {}, {cur}); |
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d_tcpg.addRewriteStep( |
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cur, curw, &d_wintroPf, true, PfRule::ASSUME, true); |
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} |
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else |
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{ |
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// A term whose witness form is different from itself, recurse. |
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// It should be the case that cur has children, since the witness |
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// form of constants are themselves. |
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Assert(cur.getNumChildren() > 0); |
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if (cur.hasOperator()) |
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{ |
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visit.push_back(cur.getOperator()); |
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} |
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visit.insert(visit.end(), cur.begin(), cur.end()); |
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} |
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} |
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} |
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} while (!visit.empty()); |
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return tw; |
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} |
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bool WitnessFormGenerator::requiresWitnessFormTransform(Node t, Node s) const |
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{ |
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return theory::Rewriter::rewrite(t) != theory::Rewriter::rewrite(s); |
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} |
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bool WitnessFormGenerator::requiresWitnessFormIntro(Node t) const |
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{ |
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Node tr = theory::Rewriter::rewrite(t); |
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return !tr.isConst() || !tr.getConst<bool>(); |
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} |
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const std::unordered_set<Node>& WitnessFormGenerator::getWitnessFormEqs() const |
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{ |
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return d_eqs; |
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} |
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ProofGenerator* WitnessFormGenerator::convertExistsInternal(Node exists) |
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{ |
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Assert(exists.getKind() == kind::EXISTS); |
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if (exists[0].getNumChildren() == 1 && exists[1].getKind() == kind::EQUAL |
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&& exists[1][0] == exists[0][0]) |
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{ |
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Node tpurified = exists[1][1]; |
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Trace("witness-form") << "convertExistsInternal: infer purification " |
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<< exists << " for " << tpurified << std::endl; |
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// ------ REFL |
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// t = t |
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// ---------------- EXISTS_INTRO |
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// exists x. x = t |
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// The concluded existential is then used to construct the witness term |
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// via witness intro. |
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Node teq = tpurified.eqNode(tpurified); |
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d_pskPf.addStep(teq, PfRule::REFL, {}, {tpurified}); |
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d_pskPf.addStep(exists, PfRule::EXISTS_INTRO, {teq}, {exists}); |
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return &d_pskPf; |
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} |
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return nullptr; |
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} |
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} // namespace smt |
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} // namespace cvc5 |