(defparameter *shape* (klass () area))
(defparameter *circle* (klass (*shape*) radius))
  
(defprop radius)
  
(defmeth area *circle* (u)
	 (* pi (expt (radius u) 2)))
  
(defun !circle ()
  (let ((c (inst0 *circle*)))
    (setf (radius c) 2)
    (area c)))