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.bdds.datastructures;
  
  import org.logicng.formulas.Variable;
  
  import java.util.Collections;
  import java.util.HashSet;
  import java.util.Objects;
  import java.util.Set;
  
  /**
   * A node in a BDD.
   * @version 1.4.0
   * @since 1.4.0
   */
  public final class BDDInnerNode implements BDDNode {
  
      private final Variable var;
      private final BDDNode low;
      private final BDDNode high;
  
      /**
       * Constructor for a new inner BDD node holding a variable.
       * @param var  the variable
       * @param low  the low child node
       * @param high the high child node
       */
      public BDDInnerNode(final Variable var, final BDDNode low, final BDDNode high) {
          this.var = var;
          this.low = low;
          this.high = high;
      }
  
      @Override
      public Variable label() {
          return this.var;
      }
  
      @Override
      public boolean isInnerNode() {
          return true;
      }
  
      @Override
      public BDDNode low() {
          return this.low;
      }
  
      @Override
      public BDDNode high() {
          return this.high;
      }
  
      @Override
      public Set<BDDNode> nodes() {
          final Set<BDDNode> res = new HashSet<>(Collections.singleton(this));
          res.addAll(this.low.nodes());
          res.addAll(this.high.nodes());
          return res;
      }
  
      @Override
      public int hashCode() {
          return Objects.hash(this.var, this.low, this.high);
      }
  
      @Override
      public boolean equals(final Object other) {
          if (this == other) {
              return true;
          }
          if (other instanceof BDDInnerNode) {
              final BDDInnerNode o = (BDDInnerNode) other;
              return Objects.equals(this.var, o.var)
                      && Objects.equals(this.low, o.low)
                      && Objects.equals(this.high, o.high);
          }
          return false;
      }
  
      @Override
      public String toString() {
          return "<" + this.var + " | low=" + this.low + " high=" + this.high + ">";
      }
  }
  