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GCC Code Coverage Report
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File:	src/theory/quantifiers/cegqi/ceg_bv_instantiator.cpp	Lines:	299	351	85.2 %
Date:	2021-09-07	Branches:	658	1684	39.1 %

/******************************************************************************
 * Top contributors (to current version):
 *   Andrew Reynolds, Mathias Preiner, Andres Noetzli
 *
 * 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.
 * ****************************************************************************
 *
 * Implementation of ceg_bv_instantiator
 */

#include "theory/quantifiers/cegqi/ceg_bv_instantiator.h"

#include <stack>
#include "expr/skolem_manager.h"
#include "options/quantifiers_options.h"
#include "theory/bv/theory_bv_utils.h"
#include "theory/quantifiers/cegqi/ceg_bv_instantiator_utils.h"
#include "theory/rewriter.h"
#include "util/bitvector.h"
#include "util/random.h"

using namespace std;
using namespace cvc5::kind;

namespace cvc5 {
namespace theory {
namespace quantifiers {

// this class can be used to query the model value through the CegInstaniator
// class
class CegInstantiatorBvInverterQuery : public BvInverterQuery
{
 public:
  CegInstantiatorBvInverterQuery(CegInstantiator* ci)
      : BvInverterQuery(), d_ci(ci)
  {
  }
  ~CegInstantiatorBvInverterQuery() {}
  /** return the model value of n */
  Node getModelValue(Node n) override { return d_ci->getModelValue(n); }
  /** get bound variable of type tn */
  Node getBoundVariable(TypeNode tn) override
  {
    return d_ci->getBoundVariable(tn);
  }

 protected:
  // pointer to class that is able to query model values
  CegInstantiator* d_ci;
};

BvInstantiator::BvInstantiator(TypeNode tn, BvInverter* inv)
    : Instantiator(tn), d_inverter(inv), d_inst_id_counter(0)
{
  // The inverter utility d_inverter is global to all BvInstantiator classes.
  // This must be global since we need to:
  // * process Skolem functions properly across multiple variables within the
  // same quantifier
  // * cache Skolem variables uniformly across multiple quantified formulas
}

BvInstantiator::~BvInstantiator() {}
void BvInstantiator::reset(CegInstantiator* ci,
                           SolvedForm& sf,
                           Node pv,
                           CegInstEffort effort)
{
  d_inst_id_counter = 0;
  d_var_to_inst_id.clear();
  d_inst_id_to_term.clear();
  d_inst_id_to_alit.clear();
  d_var_to_curr_inst_id.clear();
  d_alit_to_model_slack.clear();
}

void BvInstantiator::processLiteral(CegInstantiator* ci,
                                    SolvedForm& sf,
                                    Node pv,
                                    Node lit,
                                    Node alit,
                                    CegInstEffort effort)
{
  Assert(d_inverter != NULL);
  // find path to pv
  std::vector<unsigned> path;
  Node sv = d_inverter->getSolveVariable(pv.getType());
  Node pvs = ci->getModelValue(pv);
  Trace("cegqi-bv") << "Get path to " << pv << " : " << lit << std::endl;
  Node slit =
      d_inverter->getPathToPv(lit, pv, sv, pvs, path, options::cegqiBvSolveNl());
  if (!slit.isNull())
  {
    CegInstantiatorBvInverterQuery m(ci);
    unsigned iid = d_inst_id_counter;
    Trace("cegqi-bv") << "Solve lit to bv inverter : " << slit << std::endl;
    Node inst = d_inverter->solveBvLit(sv, slit, path, &m);
    if (!inst.isNull())
    {
      inst = Rewriter::rewrite(inst);
      if (inst.isConst() || !ci->hasNestedQuantification())
      {
        Trace("cegqi-bv") << "...solved form is " << inst << std::endl;
        // store information for id and increment
        d_var_to_inst_id[pv].push_back(iid);
        d_inst_id_to_term[iid] = inst;
        d_inst_id_to_alit[iid] = alit;
        d_inst_id_counter++;
      }
    }
    else
    {
      Trace("cegqi-bv") << "...failed to solve." << std::endl;
    }
  }
  else
  {
    Trace("cegqi-bv") << "...no path." << std::endl;
  }
}

bool BvInstantiator::hasProcessAssertion(CegInstantiator* ci,
                                         SolvedForm& sf,
                                         Node pv,
                                         CegInstEffort effort)
{
  return true;
}

Node BvInstantiator::hasProcessAssertion(CegInstantiator* ci,
                                         SolvedForm& sf,
                                         Node pv,
                                         Node lit,
                                         CegInstEffort effort)
{
  if (effort == CEG_INST_EFFORT_FULL)
  {
    // always use model values at full effort
    return Node::null();
  }
  Node atom = lit.getKind() == NOT ? lit[0] : lit;
  bool pol = lit.getKind() != NOT;
  Kind k = atom.getKind();
  if (k != EQUAL && k != BITVECTOR_ULT && k != BITVECTOR_SLT)
  {
    // others are unhandled
    return Node::null();
  }
  else if (!atom[0].getType().isBitVector())
  {
    return Node::null();
  }
  else if (options::cegqiBvIneqMode() == options::CegqiBvIneqMode::KEEP
           || (pol && k == EQUAL))
  {
    return lit;
  }
  NodeManager* nm = NodeManager::currentNM();
  Node s = atom[0];
  Node t = atom[1];

  Node sm = ci->getModelValue(s);
  Node tm = ci->getModelValue(t);
  Assert(!sm.isNull() && sm.isConst());
  Assert(!tm.isNull() && tm.isConst());
  Trace("cegqi-bv") << "Model value: " << std::endl;
  Trace("cegqi-bv") << "   " << s << " " << k << " " << t << " is "
                    << std::endl;
  Trace("cegqi-bv") << "   " << sm << " <> " << tm << std::endl;

  Node ret;
  if (options::cegqiBvIneqMode() == options::CegqiBvIneqMode::EQ_SLACK)
  {
    // if using slack, we convert constraints to a positive equality based on
    // the current model M, e.g.:
    //   (not) s ~ t  --->  s = t + ( s^M - t^M )
    if (sm != tm)
    {
      Node slack = Rewriter::rewrite(nm->mkNode(BITVECTOR_SUB, sm, tm));
      Assert(slack.isConst());
      // remember the slack value for the asserted literal
      d_alit_to_model_slack[lit] = slack;
      ret = nm->mkNode(EQUAL, s, nm->mkNode(BITVECTOR_ADD, t, slack));
      Trace("cegqi-bv") << "Slack is " << slack << std::endl;
    }
    else
    {
      ret = s.eqNode(t);
    }
  }
  else
  {
    // turn disequality into an inequality
    // e.g. s != t becomes s < t or t < s
    if (k == EQUAL)
    {
      if (Random::getRandom().pickWithProb(0.5))
      {
        std::swap(s, t);
      }
      pol = true;
    }
    // otherwise, we optimistically solve for the boundary point of an
    // inequality, for example:
    //   for s < t, we solve s+1 = t
    //   for ~( s < t ), we solve s = t
    // notice that this equality does not necessarily hold in the model, and
    // hence the corresponding instantiation strategy is not guaranteed to be
    // monotonic.
    if (!pol)
    {
      ret = s.eqNode(t);
    }
    else
    {
      Node bv_one = bv::utils::mkOne(bv::utils::getSize(s));
      ret = nm->mkNode(BITVECTOR_ADD, s, bv_one).eqNode(t);
    }
  }
  Trace("cegqi-bv") << "Process " << lit << " as " << ret << std::endl;
  return ret;
}

bool BvInstantiator::processAssertion(CegInstantiator* ci,
                                      SolvedForm& sf,
                                      Node pv,
                                      Node lit,
                                      Node alit,
                                      CegInstEffort effort)
{
  // if option enabled, use approach for word-level inversion for BV
  // instantiation
  if (options::cegqiBv())
  {
    // get the best rewritten form of lit for solving for pv
    //   this should remove instances of non-invertible operators, and
    //   "linearize" lit with respect to pv as much as possible
    Node rlit = rewriteAssertionForSolvePv(ci, pv, lit);
    if (Trace.isOn("cegqi-bv"))
    {
      Trace("cegqi-bv") << "BvInstantiator::processAssertion : solve " << pv
                        << " in " << lit << std::endl;
      if (lit != rlit)
      {
        Trace("cegqi-bv") << "...rewritten to " << rlit << std::endl;
      }
    }
    if (!rlit.isNull())
    {
      processLiteral(ci, sf, pv, rlit, alit, effort);
    }
  }
  return false;
}

bool BvInstantiator::useModelValue(CegInstantiator* ci,
                                   SolvedForm& sf,
                                   Node pv,
                                   CegInstEffort effort)
{
  return effort < CEG_INST_EFFORT_FULL || options::cegqiFullEffort();
}

bool BvInstantiator::processAssertions(CegInstantiator* ci,
                                       SolvedForm& sf,
                                       Node pv,
                                       CegInstEffort effort)
{
  std::unordered_map<Node, std::vector<unsigned>>::iterator iti =
      d_var_to_inst_id.find(pv);
  if (iti == d_var_to_inst_id.end())
  {
    // no bounds
    return false;
  }
  Trace("cegqi-bv") << "BvInstantiator::processAssertions for " << pv
                    << std::endl;
  // if interleaving, do not do inversion half the time
  if (options::cegqiBvInterleaveValue() && Random::getRandom().pickWithProb(0.5))
  {
    Trace("cegqi-bv") << "...do not do instantiation for " << pv
                      << " (skip, based on heuristic)" << std::endl;
  }
  bool firstVar = sf.empty();
  // get inst id list
  if (Trace.isOn("cegqi-bv"))
  {
    Trace("cegqi-bv") << "  " << iti->second.size()
                      << " candidate instantiations for " << pv << " : "
                      << std::endl;
    if (firstVar)
    {
      Trace("cegqi-bv") << "  ...this is the first variable" << std::endl;
    }
  }
  // until we have a model-preserving selection function for BV, this must
  // be heuristic (we only pick one literal)
  // hence we randomize the list
  // this helps robustness, since picking the same literal every time may
  // lead to a stream of value instantiations, whereas with randomization
  // we may find an invertible literal that leads to a useful instantiation.
  std::shuffle(iti->second.begin(), iti->second.end(), Random::getRandom());

  if (Trace.isOn("cegqi-bv"))
  {
    for (unsigned j = 0, size = iti->second.size(); j < size; j++)
    {
      unsigned inst_id = iti->second[j];
      Assert(d_inst_id_to_term.find(inst_id) != d_inst_id_to_term.end());
      Node inst_term = d_inst_id_to_term[inst_id];
      Assert(d_inst_id_to_alit.find(inst_id) != d_inst_id_to_alit.end());
      Node alit = d_inst_id_to_alit[inst_id];

      // get the slack value introduced for the asserted literal
      Node curr_slack_val;
      std::unordered_map<Node, Node>::iterator itms =
          d_alit_to_model_slack.find(alit);
      if (itms != d_alit_to_model_slack.end())
      {
        curr_slack_val = itms->second;
      }

      // debug printing
      Trace("cegqi-bv") << "   [" << j << "] : ";
      Trace("cegqi-bv") << inst_term << std::endl;
      if (!curr_slack_val.isNull())
      {
        Trace("cegqi-bv") << "   ...with slack value : " << curr_slack_val
                          << std::endl;
      }
      Trace("cegqi-bv-debug") << "   ...from : " << alit << std::endl;
      Trace("cegqi-bv") << std::endl;
    }
  }

  // Now, try all instantiation ids we want to try
  // Typically we try only one, otherwise worst-case performance
  // for constructing instantiations is exponential on the number of
  // variables in this quantifier prefix.
  bool ret = false;
  bool tryMultipleInst = firstVar && options::cegqiMultiInst();
  bool revertOnSuccess = tryMultipleInst;
  for (unsigned j = 0, size = iti->second.size(); j < size; j++)
  {
    unsigned inst_id = iti->second[j];
    Assert(d_inst_id_to_term.find(inst_id) != d_inst_id_to_term.end());
    Node inst_term = d_inst_id_to_term[inst_id];
    Node alit = d_inst_id_to_alit[inst_id];
    // try instantiation pv -> inst_term
    TermProperties pv_prop_bv;
    Trace("cegqi-bv") << "*** try " << pv << " -> " << inst_term << std::endl;
    d_var_to_curr_inst_id[pv] = inst_id;
    ci->markSolved(alit);
    if (ci->constructInstantiationInc(
            pv, inst_term, pv_prop_bv, sf, revertOnSuccess))
    {
      ret = true;
    }
    ci->markSolved(alit, false);
    // we are done unless we try multiple instances
    if (!tryMultipleInst)
    {
      break;
    }
  }
  if (ret)
  {
    return true;
  }
  Trace("cegqi-bv") << "...failed to add instantiation for " << pv << std::endl;
  d_var_to_curr_inst_id.erase(pv);

  return false;
}

Node BvInstantiator::rewriteAssertionForSolvePv(CegInstantiator* ci,
                                                Node pv,
                                                Node lit)
{
  // result of rewriting the visited term
  std::stack<std::unordered_map<TNode, Node>> visited;
  visited.push(std::unordered_map<TNode, Node>());
  // whether the visited term contains pv
  std::unordered_map<Node, bool> visited_contains_pv;
  std::unordered_map<TNode, Node>::iterator it;
  std::unordered_map<TNode, Node> curr_subs;
  std::stack<std::stack<TNode> > visit;
  TNode cur;
  visit.push(std::stack<TNode>());
  visit.top().push(lit);
  do
  {
    cur = visit.top().top();
    visit.top().pop();
    it = visited.top().find(cur);

    if (it == visited.top().end())
    {
      std::unordered_map<TNode, Node>::iterator itc = curr_subs.find(cur);
      if (itc != curr_subs.end())
      {
        visited.top()[cur] = itc->second;
      }
      else
      {
        if (cur.getKind() == WITNESS)
        {
          // must replace variables of choice functions
          // with new variables to avoid variable
          // capture when considering substitutions
          // with multiple literals.
          Node bv = ci->getBoundVariable(cur[0][0].getType());
          // should not have captured variables
          Assert(curr_subs.find(cur[0][0]) == curr_subs.end());
          curr_subs[cur[0][0]] = bv;
          // we cannot cache the results of subterms
          // of this witness expression since we are
          // now in the context { cur[0][0] -> bv },
          // hence we push a context here
          visited.push(std::unordered_map<TNode, Node>());
          visit.push(std::stack<TNode>());
        }
        visited.top()[cur] = Node::null();
        visit.top().push(cur);
        for (unsigned i = 0; i < cur.getNumChildren(); i++)
        {
          visit.top().push(cur[i]);
        }
      }
    }
    else if (it->second.isNull())
    {
      Node ret;
      bool childChanged = false;
      std::vector<Node> children;
      if (cur.getMetaKind() == kind::metakind::PARAMETERIZED)
      {
        children.push_back(cur.getOperator());
      }
      bool contains_pv = (cur == pv);
      for (unsigned i = 0; i < cur.getNumChildren(); i++)
      {
        it = visited.top().find(cur[i]);
        Assert(it != visited.top().end());
        Assert(!it->second.isNull());
        childChanged = childChanged || cur[i] != it->second;
        children.push_back(it->second);
        contains_pv = contains_pv || visited_contains_pv[cur[i]];
      }
      // careful that rewrites above do not affect whether this term contains pv
      visited_contains_pv[cur] = contains_pv;

      // rewrite the term
      ret = rewriteTermForSolvePv(pv, cur, children, visited_contains_pv);

      // return original if the above function does not produce a result
      if (ret.isNull())
      {
        if (childChanged)
        {
          ret = NodeManager::currentNM()->mkNode(cur.getKind(), children);
        }
        else
        {
          ret = cur;
        }
      }

      /* We need to update contains_pv also for rewritten nodes, since
       * the normalizePv* functions rely on the information if pv occurs in a
       * rewritten node or not. */
      if (ret != cur)
      {
        contains_pv = (ret == pv);
        for (unsigned i = 0, size = ret.getNumChildren(); i < size; ++i)
        {
          contains_pv = contains_pv || visited_contains_pv[ret[i]];
        }
        visited_contains_pv[ret] = contains_pv;
      }

      // if was witness, pop context
      if (cur.getKind() == WITNESS)
      {
        Assert(curr_subs.find(cur[0][0]) != curr_subs.end());
        curr_subs.erase(cur[0][0]);
        visited.pop();
        visit.pop();
        Assert(visited.size() == visit.size());
        Assert(!visit.empty());
      }

      visited.top()[cur] = ret;
    }
  } while (!visit.top().empty());
  Assert(visited.size() == 1);
  Assert(visited.top().find(lit) != visited.top().end());
  Assert(!visited.top().find(lit)->second.isNull());

  Node result = visited.top()[lit];

  if (Trace.isOn("cegqi-bv-nl"))
  {
    std::vector<TNode> trace_visit;
    std::unordered_set<TNode> trace_visited;

    trace_visit.push_back(result);
    do
    {
      cur = trace_visit.back();
      trace_visit.pop_back();

      if (trace_visited.find(cur) == trace_visited.end())
      {
        trace_visited.insert(cur);
        trace_visit.insert(trace_visit.end(), cur.begin(), cur.end());
      }
      else if (cur == pv)
      {
        Trace("cegqi-bv-nl")
            << "NONLINEAR LITERAL for " << pv << " : " << lit << std::endl;
      }
    } while (!trace_visit.empty());
  }

  return result;
}

Node BvInstantiator::rewriteTermForSolvePv(
    Node pv,
    Node n,
    std::vector<Node>& children,
    std::unordered_map<Node, bool>& contains_pv)
{
  NodeManager* nm = NodeManager::currentNM();

  // [1] rewrite cases of non-invertible operators

  if (n.getKind() == EQUAL)
  {
    TNode lhs = children[0];
    TNode rhs = children[1];

    /* rewrite: x * x = x -> x < 2 */
    if ((lhs == pv && rhs.getKind() == BITVECTOR_MULT && rhs[0] == pv
         && rhs[1] == pv)
        || (rhs == pv && lhs.getKind() == BITVECTOR_MULT && lhs[0] == pv
            && lhs[1] == pv))
    {
      return nm->mkNode(
          BITVECTOR_ULT,
          pv,
          bv::utils::mkConst(BitVector(bv::utils::getSize(pv), Integer(2))));
    }

    if (options::cegqiBvLinearize() && contains_pv[lhs] && contains_pv[rhs])
    {
      Node result = utils::normalizePvEqual(pv, children, contains_pv);
      if (!result.isNull())
      {
        Trace("cegqi-bv-nl")
            << "Normalize " << n << " to " << result << std::endl;
      }
      else
      {
        Trace("cegqi-bv-nl")
            << "Nonlinear " << n.getKind() << " " << n << std::endl;
      }
      return result;
    }
  }
  else if (n.getKind() == BITVECTOR_MULT || n.getKind() == BITVECTOR_ADD)
  {
    if (options::cegqiBvLinearize() && contains_pv[n])
    {
      Node result;
      if (n.getKind() == BITVECTOR_MULT)
      {
        result = utils::normalizePvMult(pv, children, contains_pv);
      }
      else
      {
        result = utils::normalizePvPlus(pv, children, contains_pv);
      }
      if (!result.isNull())
      {
        Trace("cegqi-bv-nl")
            << "Normalize " << n << " to " << result << std::endl;
        return result;
      }
      else
      {
        Trace("cegqi-bv-nl")
            << "Nonlinear " << n.getKind() << " " << n << std::endl;
      }
    }
  }

  // [2] try to rewrite non-linear literals -> linear literals

  return Node::null();
}

/** sort bv extract interval
 *
 * This sorts lists of bitvector extract terms where
 * ((_ extract i1 i2) t) < ((_ extract j1 j2) t)
 * if i1>j1 or i1=j1 and i2>j2.
 */
struct SortBvExtractInterval
{
  bool operator()(Node i, Node j)
  {
    Assert(i.getKind() == BITVECTOR_EXTRACT);
    Assert(j.getKind() == BITVECTOR_EXTRACT);
    BitVectorExtract ie = i.getOperator().getConst<BitVectorExtract>();
    BitVectorExtract je = j.getOperator().getConst<BitVectorExtract>();
    if (ie.d_high > je.d_high)
    {
      return true;
    }
    else if (ie.d_high == je.d_high)
    {
      Assert(ie.d_low != je.d_low);
      return ie.d_low > je.d_low;
    }
    return false;
  }
};

void BvInstantiatorPreprocess::registerCounterexampleLemma(
    Node lem, std::vector<Node>& ceVars, std::vector<Node>& auxLems)
{
  // new variables
  std::vector<Node> vars;
  // new lemmas
  std::vector<Node> new_lems;

  if (options::cegqiBvRmExtract())
  {
    NodeManager* nm = NodeManager::currentNM();
    SkolemManager* sm = nm->getSkolemManager();
    Trace("cegqi-bv-pp") << "-----remove extracts..." << std::endl;
    // map from terms to bitvector extracts applied to that term
    std::map<Node, std::vector<Node> > extract_map;
    std::unordered_set<TNode> visited;
    Trace("cegqi-bv-pp-debug2") << "Register ce lemma " << lem << std::endl;
    collectExtracts(lem, extract_map, visited);
    for (std::pair<const Node, std::vector<Node> >& es : extract_map)
    {
      // sort based on the extract start position
      std::vector<Node>& curr_vec = es.second;

      SortBvExtractInterval sbei;
      std::sort(curr_vec.begin(), curr_vec.end(), sbei);

      unsigned width = es.first.getType().getBitVectorSize();

      // list of points b such that:
      //   b>0 and we must start a segment at (b-1)  or  b==0
      std::vector<unsigned> boundaries;
      boundaries.push_back(width);
      boundaries.push_back(0);

      Trace("cegqi-bv-pp") << "For term " << es.first << " : " << std::endl;
      for (unsigned i = 0, size = curr_vec.size(); i < size; i++)
      {
        Trace("cegqi-bv-pp") << "  " << i << " : " << curr_vec[i] << std::endl;
        BitVectorExtract e =
            curr_vec[i].getOperator().getConst<BitVectorExtract>();
        if (std::find(boundaries.begin(), boundaries.end(), e.d_high + 1)
            == boundaries.end())
        {
          boundaries.push_back(e.d_high + 1);
        }
        if (std::find(boundaries.begin(), boundaries.end(), e.d_low)
            == boundaries.end())
        {
          boundaries.push_back(e.d_low);
        }
      }
      std::sort(boundaries.rbegin(), boundaries.rend());

      // make the extract variables
      std::vector<Node> children;
      for (unsigned i = 1; i < boundaries.size(); i++)
      {
        Assert(boundaries[i - 1] > 0);
        Node ex = bv::utils::mkExtract(
            es.first, boundaries[i - 1] - 1, boundaries[i]);
        Node var =
            sm->mkDummySkolem("ek",
                              ex.getType(),
                              "variable to represent disjoint extract region");
        children.push_back(var);
        vars.push_back(var);
      }

      Node conc = nm->mkNode(kind::BITVECTOR_CONCAT, children);
      Assert(conc.getType() == es.first.getType());
      Node eq_lem = conc.eqNode(es.first);
      Trace("cegqi-bv-pp") << "Introduced : " << eq_lem << std::endl;
      new_lems.push_back(eq_lem);
      Trace("cegqi-bv-pp") << "...finished processing extracts for term "
                           << es.first << std::endl;
    }
    Trace("cegqi-bv-pp") << "-----done remove extracts" << std::endl;
  }

  if (!vars.empty())
  {
    // could try applying subs -> vars here
    // in practice, this led to worse performance

    Trace("cegqi-bv-pp") << "Adding " << new_lems.size() << " lemmas..."
                         << std::endl;
    auxLems.insert(auxLems.end(), new_lems.begin(), new_lems.end());
    Trace("cegqi-bv-pp") << "Adding " << vars.size() << " variables..."
                         << std::endl;
    ceVars.insert(ceVars.end(), vars.begin(), vars.end());
  }
}

void BvInstantiatorPreprocess::collectExtracts(
    Node lem,
    std::map<Node, std::vector<Node>>& extract_map,
    std::unordered_set<TNode>& visited)
{
  std::vector<TNode> visit;
  TNode cur;
  visit.push_back(lem);
  do
  {
    cur = visit.back();
    visit.pop_back();
    if (visited.find(cur) == visited.end())
    {
      visited.insert(cur);
      if (cur.getKind() != FORALL)
      {
        if (cur.getKind() == BITVECTOR_EXTRACT)
        {
          if (cur[0].getKind() == INST_CONSTANT)
          {
            extract_map[cur[0]].push_back(cur);
          }
        }

        for (const Node& nc : cur)
        {
          visit.push_back(nc);
        }
      }
    }
  } while (!visit.empty());
}

}  // namespace quantifiers
}  // namespace theory
}  // namespace cvc5

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