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.knowledgecompilation.dnnf;
  
  import org.logicng.formulas.Formula;
  import org.logicng.formulas.Variable;
  import org.logicng.knowledgecompilation.dnnf.datastructures.Dnnf;
  import org.logicng.knowledgecompilation.dnnf.datastructures.dtree.MinFillDTreeGenerator;
  import org.logicng.transformations.cnf.CNFSubsumption;
  import org.logicng.transformations.simplification.BackboneSimplifier;
  
  import java.util.SortedSet;
  import java.util.TreeSet;
  
  /**
   * A DNNF factory that can be used to compute DNNFs from formulas.
   * @version 2.0.0
   * @since 2.0.0
   */
  public class DnnfFactory {
  
      protected final BackboneSimplifier backboneSimplifier;
      protected final CNFSubsumption subsumption;
  
      /**
       * Constructs a new DNNF factory instance.
       */
      public DnnfFactory() {
          this.backboneSimplifier = BackboneSimplifier.get();
          this.subsumption = CNFSubsumption.get();
      }
  
      /**
       * Compiles the given formula to a DNNF instance.
       * @param formula the formula
       * @return the compiled DNNF
       */
      public Dnnf compile(final Formula formula) {
          final SortedSet<Variable> originalVariables = new TreeSet<>(formula.variables());
          final Formula cnf = formula.cnf();
          originalVariables.addAll(cnf.variables());
          final Formula simplifedFormula = simplifyFormula(cnf);
          final DnnfCompiler compiler = new DnnfCompiler(simplifedFormula);
          final Formula dnnf = compiler.compile(new MinFillDTreeGenerator());
          return new Dnnf(originalVariables, dnnf);
      }
  
      protected Formula simplifyFormula(final Formula formula) {
          return formula.transform(this.backboneSimplifier).transform(this.subsumption);
      }
  }
  