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.transformations;
  
  import org.logicng.datastructures.Assignment;
  import org.logicng.formulas.Formula;
  import org.logicng.formulas.FormulaFactory;
  import org.logicng.formulas.Literal;
  import org.logicng.solvers.MiniSat;
  import org.logicng.solvers.SATSolver;
  import org.logicng.solvers.functions.ModelEnumerationFunction;
  import org.logicng.util.FormulaHelper;
  
  import java.util.ArrayList;
  import java.util.List;
  import java.util.SortedSet;
  
  /**
   * Superclass for canonical normal form enumeration (CNF or DNF) via enumeration of the falsifying/satisfying assignments.
   * @version 2.3.0
   * @since 2.3.0
   */
  public abstract class CanonicalEnumeration {
  
      /**
       * Constructs the canonical CNF/DNF of the given formula by enumerating the falsifying/satisfying assignments.
       * @param formula the formula
       * @param cnf     {@code true} if the canonical CNF should be computed, {@code false} if the canonical DNF should be computed
       * @return the canonical normal form (CNF or DNF) of the formula
       */
      protected static Formula compute(final Formula formula, final boolean cnf) {
          final FormulaFactory f = formula.factory();
          final SATSolver solver = MiniSat.miniSat(f);
          solver.add(cnf ? formula.negate() : formula);
          final List<Assignment> enumeration = solver.execute(ModelEnumerationFunction.builder().build());
          if (enumeration.isEmpty()) {
              return f.constant(cnf);
          }
          final List<Formula> ops = new ArrayList<>();
          for (final Assignment a : enumeration) {
              final SortedSet<Literal> literals = a.literals();
              final Formula term = cnf ? f.or(FormulaHelper.negate(literals, ArrayList::new)) : f.and(a.literals());
              ops.add(term);
          }
          return cnf ? f.and(ops) : f.or(ops);
      }
  }
  