code: ///////////////////////////////////////////////////////////////////////////
  //                   __                _      _   ________               //
  //                  / /   ____  ____ _(_)____/ | / / ____/               //
  //                 / /   / __ \/ __ `/ / ___/  |/ / / __                 //
  //                / /___/ /_/ / /_/ / / /__/ /|  / /_/ /                 //
  //               /_____/\____/\__, /_/\___/_/ |_/\____/                  //
  //                           /____/                                      //
  //                                                                       //
  //               The Next Generation Logic Library                       //
  //                                                                       //
  ///////////////////////////////////////////////////////////////////////////
  //                                                                       //
  //  Copyright 2015-20xx Christoph Zengler                                //
  //                                                                       //
  //  Licensed under the Apache License, Version 2.0 (the "License");      //
  //  you may not use this file except in compliance with the License.     //
  //  You may obtain a copy of the License at                              //
  //                                                                       //
  //  http://www.apache.org/licenses/LICENSE-2.0                           //
  //                                                                       //
  //  Unless required by applicable law or agreed to in writing, software  //
  //  distributed under the License is distributed on an "AS IS" BASIS,    //
  //  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or      //
  //  implied.  See the License for the specific language governing        //
  //  permissions and limitations under the License.                       //
  //                                                                       //
  ///////////////////////////////////////////////////////////////////////////
  
  package org.logicng.solvers.functions;
  
  import static org.logicng.datastructures.Tristate.TRUE;
  
  import org.logicng.collections.LNGVector;
  import org.logicng.datastructures.Tristate;
  import org.logicng.formulas.CFalse;
  import org.logicng.formulas.CType;
  import org.logicng.formulas.Formula;
  import org.logicng.formulas.FormulaFactory;
  import org.logicng.formulas.Literal;
  import org.logicng.formulas.Variable;
  import org.logicng.solvers.MiniSat;
  import org.logicng.solvers.SATSolver;
  import org.logicng.solvers.datastructures.MSClause;
  import org.logicng.solvers.datastructures.MSVariable;
  
  import java.util.ArrayList;
  import java.util.LinkedHashSet;
  import java.util.List;
  import java.util.Set;
  import java.util.function.Consumer;
  
  /**
   * A solver function for getting the current formula on the solver.
   * <p>
   * Note that this formula is usually syntactically different to the
   * formulas which were actually added to the solver, since the formulas
   * are added as CNF and may be simplified or even removed depending on
   * the state of the solver. Furthermore, the solver might add learnt
   * clauses or propagate literals.
   * <p>
   * If the formula on the solver is known to be unsatisfiable, this
   * function will add {@link CFalse falsum} to the returned set of
   * formulas. However, as long as {@link SATSolver#sat()} was not called
   * on the current solver state, the absence of {@link CFalse falsum}
   * does not imply that the formula is satisfiable.
   * <p>
   * Also note that formulas are not added to the solver as soon as the
   * solver is known be unsatisfiable.
   * @version 2.0.0
   * @since 2.0.0
   */
  public final class FormulaOnSolverFunction implements SolverFunction<Set<Formula>> {
  
      private final static FormulaOnSolverFunction INSTANCE = new FormulaOnSolverFunction();
  
      /**
       * Private empty constructor.  Singleton class.
       */
      private FormulaOnSolverFunction() {
          // Intentionally left empty
      }
  
      /**
       * Returns the singleton of the function.
       * @return the function instance
       */
      public static FormulaOnSolverFunction get() {
          return INSTANCE;
      }
  
      @Override
      public Set<Formula> apply(final MiniSat solver, final Consumer<Tristate> resultSetter) {
          final FormulaFactory f = solver.factory();
          final Set<Formula> formulas = new LinkedHashSet<>();
          for (final MSClause clause : solver.underlyingSolver().clauses()) {
              final List<Literal> lits = new ArrayList<>();
              for (int i = 0; i < clause.size(); i++) {
                  final int litInt = clause.get(i);
                  lits.add(f.literal(solver.underlyingSolver().nameForIdx(litInt >> 1), (litInt & 1) != 1));
              }
              if (!clause.isAtMost()) {
                  formulas.add(f.clause(lits));
              } else {
                  final int rhs = clause.size() + 1 - clause.atMostWatchers();
                  final List<Variable> vars = new ArrayList<>();
                  for (final Literal lit : lits) {
                      vars.add(lit.variable());
                  }
                  formulas.add(f.cc(CType.LE, rhs, vars));
              }
          }
          final LNGVector<MSVariable> variables = solver.underlyingSolver().variables();
          for (int i = 0; i < variables.size(); i++) {
              final MSVariable var = variables.get(i);
              if (var.level() == 0) {
                  formulas.add(f.literal(solver.underlyingSolver().nameForIdx(i), var.assignment() == TRUE));
              }
          }
          if (!solver.underlyingSolver().ok()) {
              formulas.add(f.falsum());
          }
          return formulas;
      }
  }
  