>
>Thanks, Mark.  I'll dig into it.  Perhaps there will be something about
>unification.  I've never heard of that term before.

I'll attempt a definition: Unification is the process of mapping two 
forms (e.g., equations) onto one another such that variables (in the 
form) are set to appropriate values and constraints are maintained. 
The process may involve backtracking, and can also end in failure (if 
no match is possible).

I did some web-hunting and this page seems like a reasonable intro to 
unification:

http://www.ccs.neu.edu/home/arthur/unif.html

I first learned about it reading Patrick Winston's first book on Lisp 
-- I remember typing in the code and poking at it forever trying to 
figure out how it was working.  I think that the best description of 
the algorithm, though, is in Brian Harvey's "Computer Science Logo 
Style" series (Volume 3, I think).  (In general, next to "Structure 
and Interpretation of Computer Programs," Harvey's books are my 
favorite CS texts.)

Mark

--------------------------
Mark Guzdial : Georgia Tech : College of Computing : Atlanta, GA 30332-0280
Associate Professor - Learning Sciences & Technologies.
Collaborative Software Lab - http://coweb.cc.gatech.edu/csl/
(404) 894-5618 : Fax (404) 894-0673 : guzdial at cc.gatech.edu
http://www.cc.gatech.edu/gvu/people/Faculty/Mark.Guzdial.html