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;
  
  import org.logicng.formulas.CType;
  import org.logicng.formulas.Constant;
  import org.logicng.formulas.Formula;
  import org.logicng.formulas.FormulaFactory;
  import org.logicng.formulas.Literal;
  import org.logicng.formulas.Variable;
  
  public abstract class TestWithExampleFormulas {
      protected final FormulaFactory f = new FormulaFactory();
      protected final FormulaFactory g = new FormulaFactory();
  
      // Constants
      protected final Constant TRUE = this.f.verum();
      protected final Constant FALSE = this.f.falsum();
  
      // Literals
      protected final Variable A = this.f.variable("a");
      protected final Variable B = this.f.variable("b");
      protected final Variable C = this.f.variable("c");
      protected final Variable D = this.f.variable("d");
      protected final Variable X = this.f.variable("x");
      protected final Variable Y = this.f.variable("y");
      protected final Literal NA = this.f.literal("a", false);
      protected final Literal NB = this.f.literal("b", false);
      protected final Literal NX = this.f.literal("x", false);
      protected final Literal NY = this.f.literal("y", false);
  
      // Disjunctions
      protected final Formula OR1 = this.f.or(this.X, this.Y);
      protected final Formula OR2 = this.f.or(this.NX, this.NY);
      protected final Formula OR3 = this.f.or(this.f.and(this.A, this.B), this.f.and(this.NA, this.NB));
  
      // Conjunctions
      protected final Formula AND1 = this.f.and(this.A, this.B);
      protected final Formula AND2 = this.f.and(this.NA, this.NB);
      protected final Formula AND3 = this.f.and(this.OR1, this.OR2);
  
      // Negations
      protected final Formula NOT1 = this.f.not(this.AND1);
      protected final Formula NOT2 = this.f.not(this.OR1);
  
      // Implications
      protected final Formula IMP1 = this.f.implication(this.A, this.B);
      protected final Formula IMP2 = this.f.implication(this.NA, this.NB);
      protected final Formula IMP3 = this.f.implication(this.AND1, this.OR1);
      protected final Formula IMP4 = this.f.implication(this.f.equivalence(this.A, this.B), this.f.equivalence(this.NX, this.NY));
  
      // Equivalences
      protected final Formula EQ1 = this.f.equivalence(this.A, this.B);
      protected final Formula EQ2 = this.f.equivalence(this.NA, this.NB);
      protected final Formula EQ3 = this.f.equivalence(this.AND1, this.OR1);
      protected final Formula EQ4 = this.f.equivalence(this.IMP1, this.IMP2);
  
      // PBCs
      private final Literal[] literals = new Literal[]{this.A, this.B, this.X};
      private final int[] coefficients = new int[]{2, -4, 3};
      protected final Formula PBC1 = this.f.pbc(CType.EQ, 2, this.literals, this.coefficients);
      protected final Formula PBC2 = this.f.pbc(CType.GT, 2, this.literals, this.coefficients);
      protected final Formula PBC3 = this.f.pbc(CType.GE, 2, this.literals, this.coefficients);
      protected final Formula PBC4 = this.f.pbc(CType.LT, 2, this.literals, this.coefficients);
      protected final Formula PBC5 = this.f.pbc(CType.LE, 2, this.literals, this.coefficients);
  }
  