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.specs;
29
30 /**
31 * That enumeration defines the possible truth value for a variable: satisfied,
32 * falsified or unknown/undefined.
33 *
34 * (that class moved from org.sat4j.minisat.core in earlier version of SAT4J).
35 *
36 * @author leberre
37 * @since 2.1
38 */
39 public class Lbool {
40
41 public static final Lbool FALSE = new Lbool("F");
42 public static final Lbool TRUE = new Lbool("T");
43 public static final Lbool UNDEFINED = new Lbool("U");
44
45 static {
46 // usual boolean rules for negation
47 FALSE.opposite = TRUE;
48 TRUE.opposite = FALSE;
49 UNDEFINED.opposite = UNDEFINED;
50 }
51
52 private Lbool(String symbol) {
53 this.symbol = symbol;
54 }
55
56 /**
57 * boolean negation.
58 *
59 * @return Boolean negation. The negation of UNDEFINED is UNDEFINED.
60 */
61 public Lbool not() {
62 return opposite;
63 }
64
65 /**
66 * Textual representation for the truth value.
67 *
68 * @return "T","F" or "U"
69 */
70 @Override
71 public String toString() {
72 return symbol;
73 }
74
75 /**
76 * The symbol representing the truth value.
77 */
78 private final String symbol;
79
80 /**
81 * the opposite truth value.
82 */
83 private Lbool opposite;
84
85 }