anchor.diff:    (error "no slots in an instance of a builtin class"))
   
   (defun slot-makunbound (object slot-name)
  -  (let* ((class (class-of object))
  -	 (slots (class-slots class))
  -	 (slot (find slot-name slots :test #'eq :key #'slot-definition-name)))
  +  (let* ((slot (find-slot object slot-name))
  +	 (class (class-of object)))
       (if (null slot)
   	(slot-missing class object slot-name 'slot-makunbound)
   	(slot-makunbound-using-class class object slot))))
  -
  -    
positive.code: 				    slot)
    (error "no slots in an instance of a builtin class"))
  
  ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
  ;;;
  ;;; SLOT-MAKUNBOUND, SLOT-MAKUNBOUND-USING-CLASS.
  
negative.code:   (error "no slots in an instance of a builtin class"))
  
  (defun slot-value (object slot-name)
    (let ((slot (find-slot object slot-name))
  	(class (class-of object)))
      (if (null slot)
  	(slot-missing class object slot-name 'slot-value)
  	(slot-value-using-class class object slot))))
  
  (defun (setf slot-value) (new-value object slot-name)
    (let ((slot (find-slot object slot-name))
  	(class (class-of object)))
      (if (null slot)
  	(slot-missing class object slot-name 'slot-value)
  	(setf (slot-value-using-class class object slot) new-value))))
  