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 }