undefmethod'ing setf forms

[Daniel A Haug <aihaug@AUSTIN.LOCKHEED.COM>]

How do I specify to undefmethod a setf method?  Specifically, something
like:

   (defmethod (setf foo) :after ((instance my-class) ...)
     ...)

I tried:

   (undefmethod (setf foo) :after (my-class))

But it doesn't seem to find the method named (setf foo).

dan haug
haug@austin.lockheed.com