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1   /*
2    * SAT4J: a SATisfiability library for Java Copyright (C) 2004-2006 Daniel Le Berre
3    * 
4    * Based on the original minisat specification from:
5    * 
6    * An extensible SAT solver. Niklas E?n and Niklas S?rensson. Proceedings of the
7    * Sixth International Conference on Theory and Applications of Satisfiability
8    * Testing, LNCS 2919, pp 502-518, 2003.
9    * 
10   * This library is free software; you can redistribute it and/or modify it under
11   * the terms of the GNU Lesser General Public License as published by the Free
12   * Software Foundation; either version 2.1 of the License, or (at your option)
13   * any later version.
14   * 
15   * This library is distributed in the hope that it will be useful, but WITHOUT
16   * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
17   * FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more
18   * details.
19   * 
20   * You should have received a copy of the GNU Lesser General Public License
21   * along with this library; if not, write to the Free Software Foundation, Inc.,
22   * 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
23   * 
24   */
25  
26  package org.sat4j.minisat.core;
27  
28  /**
29   * That enumeration defines the possible truth value for a variable: satisfied,
30   * falsified or unknown/undefined.
31   * 
32   * @author leberre
33   */
34  public enum Lbool {
35  
36      FALSE("F"), TRUE("T"), UNDEFINED("U"); //$NON-NLS-1$//$NON-NLS-2$ //$NON-NLS-3$
37  
38      static {
39          // usual boolean rules for negation
40          FALSE.opposite = TRUE;
41          TRUE.opposite = FALSE;
42          UNDEFINED.opposite = UNDEFINED;
43      }
44  
45      private Lbool(String symbol) {
46          this.symbol = symbol;
47      }
48  
49      /**
50       * boolean negation.
51       * 
52       * @return Boolean negation. The negation of UNDEFINED is UNDEFINED.
53       */
54      public Lbool not() {
55          return opposite;
56      }
57  
58      /**
59       * Textual representation for the truth value.
60       * 
61       * @return "T","F" or "U"
62       */
63      @Override
64      public String toString() {
65          return symbol;
66      }
67  
68      /**
69       * The symbol representing the truth value.
70       */
71      private final String symbol;
72  
73      /**
74       * the opposite truth value.
75       */
76      private Lbool opposite;
77  
78  }