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/*
    This file is part of JLog.

    Created by Glendon Holst for Alan Mackworth and the 
    "Computational Intelligence: A Logical Approach" text.
    
    Copyright 1998, 2000, 2002 by University of British Columbia and 
    Alan Mackworth.
    
    This notice must remain in all files which belong to, or are derived 
    from JLog.
    
    Check  or 
     for further information
    about JLog, or to contact the authors.
     
    JLog is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation; either version 2 of the License, or
    (at your option) any later version.

    JLog is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with JLog; if not, write to the Free Software
    Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
    URLs:  or 
*/
//#########################################################################
//	UnifiedVector
//#########################################################################

package ubc.cs.JLog.Foundation;

import java.lang.*;
import java.util.*;
import ubc.cs.JLog.Terms.*;

/**
* This class is used to register jVariable mapped pairs during 
* equivalence testing.
*  
* @author       Glendon Holst
* @version      %I%, %G%
*/
public class jEquivalenceMapping
{
 protected Hashtable 		variables;
 
 public jEquivalenceMapping()
 {
  variables = new Hashtable();
 };
 
 /**
  * Adds a mapping between two different variables.  Should be invoked by the 
  * jVariable during equivalence testing.
  *
  * @param v1 		a variable to pair.
  * @param v2 		the other variable in the pair.
  *
  * @return boolean	true if the variables were previously unmapped, or this is the same mapping
  *					false otherwise.
  */
 public final boolean 		mapVariablePair(jVariable v1,jVariable v2)
 {
  Object val1 = variables.get(v1);
  Object val2 = variables.get(v2);

  if (val1 == null && val2 == null)
  {
   variables.put(v1,v2);
   variables.put(v2,v1);

   return true;
  }  
  
  return (val1 == v2 && val2 == v1);
 };

};