[plt-scheme] documentation for swindle's clos?

Ciao,

I am new to MzScheme. I am looking for documentation
for "clos.ss". It seems to me that there is nothing in the
online doc at plt-scheme.org.

Can you tell me if it is possible rebind a symbol
to a generic function? If I try:

(define saved-display display)
(defgeneric display)
(defmethod (display (o <top>) . args)
  (apply saved-display o args))

(defmethod (display (o <integer>))
  (format "integer ~A~%" o)
  (newline))

I get:

add-method: wrong arity for `display', expects at-least-1;
given a method with 1

I am used to Guile's GOOPS and with it this is possible.

Thanks

-- 
Marco Maggi

"Now feel the funk blast!"
Rage Against the Machine - "Calm like a bomb"