1 /*******************************************************************************
2 * SAT4J: a SATisfiability library for Java Copyright (C) 2004, 2012 Artois University and CNRS
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 * Contributors:
28 * CRIL - initial API and implementation
29 *******************************************************************************/
30 package org.sat4j.specs;
31
32 /**
33 * That enumeration defines the possible truth value for a variable: satisfied,
34 * falsified or unknown/undefined.
35 *
36 * (that class moved from org.sat4j.minisat.core in earlier version of SAT4J).
37 *
38 * @author leberre
39 * @since 2.1
40 */
41 public final class Lbool {
42
43 public static final Lbool FALSE = new Lbool("F");
44 public static final Lbool TRUE = new Lbool("T");
45 public static final Lbool UNDEFINED = new Lbool("U");
46
47 static {
48 // usual boolean rules for negation
49 FALSE.opposite = TRUE;
50 TRUE.opposite = FALSE;
51 UNDEFINED.opposite = UNDEFINED;
52 }
53
54 private Lbool(String symbol) {
55 this.symbol = symbol;
56 }
57
58 /**
59 * boolean negation.
60 *
61 * @return Boolean negation. The negation of UNDEFINED is UNDEFINED.
62 */
63 public Lbool not() {
64 return this.opposite;
65 }
66
67 /**
68 * Textual representation for the truth value.
69 *
70 * @return "T","F" or "U"
71 */
72 @Override
73 public String toString() {
74 return this.symbol;
75 }
76
77 /**
78 * The symbol representing the truth value.
79 */
80 private final String symbol;
81
82 /**
83 * the opposite truth value.
84 */
85 private Lbool opposite;
86
87 }