private void addXref(TermPair pair) {
   SessionManager.getManager()
       .apply(
           new AddDbxrefHistoryItem(
               pair.getReferrer().getID(),
               this.makeDbxref(pair.getMaster().getID()),
               false,
               null));
 }
 /** @param pair term pair : (variable,constant) */
 public void addPair(TermPair pair) {
   pairList.add(pair);
   variables.add(pair.getX());
 }
  /** @return list of substitutes */
  public ArrayList<Term> getSubstitutes() {
    ArrayList<Term> list = new ArrayList<Term>();
    for (TermPair p : this.pairList) list.add(p.getY());

    return list;
  }
 /**
  * Copy constructor
  *
  * @param copy
  */
 public Substitution(Substitution copy) {
   pairList = new ArrayList<TermPair>(copy.getPairList());
   variables = new ArrayList<Term>();
   for (TermPair c : pairList) variables.add(c.getX());
 }
 /**
  * Constructor
  *
  * @param termPairList list of term pairs
  */
 public Substitution(ArrayList<TermPair> termPairList) {
   pairList = termPairList;
   variables = new ArrayList<Term>();
   for (TermPair c : pairList) variables.add(c.getX());
 }