n", because the unifiers
are constructed incrementally, as needed.  Here is an example
of how to do it.  Assume we have Terms t1 and t2.
<PRE>
  {
    <A HREF="unify.html">Context</A> c1 = get_context();
    <A HREF="unify.html">Context</A> c2 = get_context();
    bt = <A HREF="#unify_bt_first">unify_bt_first</A>(t1, c1, t2, c2);
    while (bt != NULL) {
      t3 = apply(t1, c1);
      t4 = apply(t2, c2);
      <Now, t3 and t4 should be identical, mod any AC or C symbols.>
      zap_term(t4);
      bt = <A 