Is there a substitute for define-method-combination?

[Timothy.Freeman@theory.cs.cmu.edu]

I want to do something that could be done fairly easily with
define-method-combination, but unfortunately PCL doesn't have
define-method-combination yet.

Is there a summary anywhere of how PCL differs from the CLOS spec?  I
spent some time trying to understand the documentation for
define-method-combination before discovering that it was
unimplemented.  I could have saved that time if I had a list of all of
the CLOS functions and macros which are not implemented in PCL.