O_ALT = 0,
	       AC_ALT,
	       COMM_ALT
             } Unif_alternative;

</PRE><HR><A NAME=intro></A><H2>Introduction</H2>
This package handles ordinary <GL>unification</GL> and <GL>matching</GL>
of terms.
The methods are probably different from what you learned in your
logic course, so pay close attention.
<P>
In situations where you consider instantiating the variables of a term
t, you will have an associated Context c.  The Context
keeps track of the terms that are substituted for the variables---
t