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:   (error "no slots in an instance of a builtin class"))
  
  (defun slot-value (object slot-name)
    (let* ((class (class-of object))
  	 (slots (class-slots class))
  	 (slot (find slot-name slots :test #'eq :key #'slot-definition-name)))
      (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* ((class (class-of object))
  	 (slots (class-slots class))
  	 (slot (find slot-name slots :test #'eq :key #'slot-definition-name)))
      (if (null slot)
  	(slot-missing class object slot-name 'slot-value)
  	(setf (slot-value-using-class class object slot) new-value))))
  
negative.code: (in-package #:sicl-clos)
  
  (defun find-slot (object slot-name)
    (let* ((class (class-of object))
  	 (slots (if (eq class *standard-class*)
  		    (standard-instance-access
  		     object *standard-class-class-slots-location*)
  		    (class-slots class)))
  	 (name-test (lambda (slot-definition)
  		      (if (eq (class-of slot-definition)
  			      *standard-effective-slot-definition*)
  			  (standard-instance-access
  			   object
  			   *standard-effective-slot-definition-name-location*)
  			  (slot-definition-name slot-definition)))))
      (find slot-name slots :test #'eq :key name-test)))
  
  ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
  ;;;
  ;;; SLOT-EXISTS-P.
  
  (defun slot-exists-p (object slot-name)
    (not (null (find-slot object slot-name))))
  
  ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
  ;;;
  