01 /* This file is part of the project "Hilbert II" - http://www.qedeq.org
02 *
03 * Copyright 2000-2011, Michael Meyling <mime@qedeq.org>.
04 *
05 * "Hilbert II" is free software; you can redistribute
06 * it and/or modify it under the terms of the GNU General Public
07 * License as published by the Free Software Foundation; either
08 * version 2 of the License, or (at your option) any later version.
09 *
10 * This program is distributed in the hope that it will be useful,
11 * but WITHOUT ANY WARRANTY; without even the implied warranty of
12 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
13 * GNU General Public License for more details.
14 */
15
16 package org.qedeq.kernel.bo.logic.wf;
17
18 import org.qedeq.kernel.bo.logic.common.ExistenceChecker;
19 import org.qedeq.kernel.bo.logic.common.FunctionKey;
20 import org.qedeq.kernel.bo.logic.common.PredicateKey;
21
22
23 /**
24 * This implementation gives always the answer <code>true</code> to the question
25 * <em>exists this predicate?</em>.
26 *
27 * @author Michael Meyling
28 */
29 public final class EverythingExists implements ExistenceChecker {
30
31 /** One and only instance. */
32 private static final ExistenceChecker ALWAYS = new EverythingExists();
33
34 /**
35 * Hidden constructor.
36 */
37 private EverythingExists() {
38 // nothing to do
39 }
40
41 public boolean predicateExists(final String name, final int arguments) {
42 return true;
43 }
44
45 public boolean predicateExists(final PredicateKey predicate) {
46 return true;
47 }
48
49 public boolean isInitialPredicate(final PredicateKey predicate) {
50 return true;
51 }
52
53 public boolean functionExists(final String name, final int arguments) {
54 return true;
55 }
56
57 public boolean functionExists(final FunctionKey function) {
58 return true;
59 }
60
61 public boolean isInitialFunction(final FunctionKey predicate) {
62 return true;
63 }
64
65 public boolean classOperatorExists() {
66 return true;
67 }
68
69 public boolean identityOperatorExists() {
70 return true;
71 }
72
73 public String getIdentityOperator() {
74 return NAME_EQUAL;
75 }
76
77 /**
78 * Get one instance of this class.
79 *
80 * @return Class instance.
81 */
82 public static final ExistenceChecker getInstance() {
83 return ALWAYS;
84 }
85
86 }
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