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.formulas;
  
  /**
   * Formula types for LogicNG.
   * @version 1.3
   * @since 1.0
   */
  public enum FType {
      PBC((byte) 0x00),
      EQUIV((byte) 0x01),
      IMPL((byte) 0x02),
      OR((byte) 0x03),
      AND((byte) 0x04),
      NOT((byte) 0x05),
      LITERAL((byte) 0x06),
      TRUE((byte) 0x07),
      FALSE((byte) 0x08);
  
      private final byte precedence;
  
      /**
       * Constructs a new formula type with a given precedence and syntax string
       * @param precedence the precedence
       */
      FType(final byte precedence) {
          this.precedence = precedence;
      }
  
      /**
       * Returns the precedence of this formula type.
       * @return the precedence of this formula type
       */
      public byte precedence() {
          return this.precedence;
      }
  
      /**
       * Returns the dual operator of the given operator, i.e. AND for OR and vice versa.
       * @param type the type (AND or OR)
       * @return the dual operator
       */
      public static FType dual(final FType type) {
          if (type != AND && type != OR) {
              throw new IllegalArgumentException("Expected type AND or OR.");
          }
          return type == AND ? OR : AND;
      }
  }
  