anchor.diff:  	     (when (null class)
   	       (error "no such method class ~s" method-class))
   	     (setf method-class class)))
  -	  ((classp method-class)
  +	  ((typep method-class 'class)
   	   nil)
   	  (t
   	   (error "method class must be a class or a name"))))
  
positive.code: 	     (when (null class)
  	       (error "no such method class ~s" method-class))
  	     (setf method-class class)))
  	  ((classp method-class)
  	   nil)
  	  (t
  	   (error "method class must be a class or a name"))))
  
negative.code: 	     (error "no such generic-function-class ~s"
  		    generic-function-class))
  	   (setf generic-function-class class)))
  	((typep generic-function-class 'class)
  	 nil)
  	(t
  	 (error "generic function class must be a class or a name")))
  