fy.html">Trail</A>.
If successful, the trail is extended (at its front) with
substitutions that were made, and trp is updated to point to
the new beginning of the trail.  If unify fails, the Contexts and
the <A HREF="unify.html">Trail</A> * are not changed.
<P>
You must make sure, before calling <A HREF="#unify">unify</A>(), that no variable v in
t1 or t2 has VARNUM(v) >= MAXVARS.  This is usually accomplished by
calling a routine that renames variables.
<P>
Here is an example how to use <A HREF="#unify">un