1 /*******************************************************************************
2 * SAT4J: a SATisfiability library for Java Copyright (C) 2004-2008 Daniel Le Berre
3 *
4 * All rights reserved. This program and the accompanying materials
5 * are made available under the terms of the Eclipse Public License v1.0
6 * which accompanies this distribution, and is available at
7 * http://www.eclipse.org/legal/epl-v10.html
8 *
9 * Alternatively, the contents of this file may be used under the terms of
10 * either the GNU Lesser General Public License Version 2.1 or later (the
11 * "LGPL"), in which case the provisions of the LGPL are applicable instead
12 * of those above. If you wish to allow use of your version of this file only
13 * under the terms of the LGPL, and not to allow others to use your version of
14 * this file under the terms of the EPL, indicate your decision by deleting
15 * the provisions above and replace them with the notice and other provisions
16 * required by the LGPL. If you do not delete the provisions above, a recipient
17 * may use your version of this file under the terms of the EPL or the LGPL.
18 *
19 * Based on the original MiniSat specification from:
20 *
21 * An extensible SAT solver. Niklas Een and Niklas Sorensson. Proceedings of the
22 * Sixth International Conference on Theory and Applications of Satisfiability
23 * Testing, LNCS 2919, pp 502-518, 2003.
24 *
25 * See www.minisat.se for the original solver in C++.
26 *
27 *******************************************************************************/
28 package org.sat4j.minisat.core;
29
30 /**
31 * That enumeration defines the possible truth value for a variable: satisfied,
32 * falsified or unknown/undefined.
33 *
34 * @author leberre
35 */
36 public class Lbool {
37
38 public static final Lbool FALSE = new Lbool("F");
39 public static final Lbool TRUE = new Lbool("T");
40 public static final Lbool UNDEFINED = new Lbool("U");
41
42 static {
43 // usual boolean rules for negation
44 FALSE.opposite = TRUE;
45 TRUE.opposite = FALSE;
46 UNDEFINED.opposite = UNDEFINED;
47 }
48
49 private Lbool(String symbol) {
50 this.symbol = symbol;
51 }
52
53 /**
54 * boolean negation.
55 *
56 * @return Boolean negation. The negation of UNDEFINED is UNDEFINED.
57 */
58 public Lbool not() {
59 return opposite;
60 }
61
62 /**
63 * Textual representation for the truth value.
64 *
65 * @return "T","F" or "U"
66 */
67 @Override
68 public String toString() {
69 return symbol;
70 }
71
72 /**
73 * The symbol representing the truth value.
74 */
75 private final String symbol;
76
77 /**
78 * the opposite truth value.
79 */
80 private Lbool opposite;
81
82 }