 checks if <A HREF="term.html">Term</A> t1 (in <A HREF="unify.html">Context</A> c1) and <A HREF="term.html">Term</A> t2
(without a <A HREF="unify.html">Context</A>) are variants, that is, if each is an instance of the other.
If successful, the unifying substitution is in <A HREF="unify.html">Context</A> c1.
The calling sequence and the use of Contexts and Trails is the same
as for <A HREF="#unify">unify</A>().
<A NAME="vars_in_trail"></A><HR><PRE><B>Ilist vars_in_trail(<A HREF="unify.html">Trail</A> tr);
</