Thanks, all, for your helpful responses! What Chris is
doing with STACK looks very similar to what I want to
do, so I think I'll try to pick up a minimal amount of
PHP, and read through his code. Spotter uses numerical
sampling rather than symbolic algebra to see if the student's
answer is correct, but there are definitely a bunch of
cases where symbolic algebra could also come in handy
in my application, and it looks like Chris has already
solved the problem of sandboxing, etc. Chris, does the
interactivity issue just not come up in your application,
since you're basically just typesetting equations and
using Maxima to test whether expressions are equal or
not? I wonder what integrals.com does when you feed it
an integral that can't be evaluated without knowing if
a certain constant is positive, or is an integer? One
thing that would probably cut out a lot of these difficulties
would be simply to have the integral-computing service
only accept integrals that don't have symbolic constants
in them. Generally that just means that the user has to
do an additional step of substitution.
Ben