math functions, derrivatives

[tusneem@ecn.purdue.edu (Irfan Tusneem)]

     Has anyone written math functions to take derrivatives of expressions?
I am making a small math package to multiply, divide, add, sub numbers
in infix notation.  I would like to add a derivative function also.
The one I currently use is very simple (x to power y, x exp y).
If someone has written code to do this in lisp I would appreciate it if
you could send me a copy.

Irfan Tusneem
tusneem@en.ecn.purdue.edu