anchor.diff:  
   (defun make-direct-slot-definition (&rest initargs
   				    &key &allow-other-keys)
  -  (let* ((defs *effective-slots-standard-direct-slot-definition*)
  +  (let* ((defs (find-effective-slots 'standard-direct-slot-definition))
   	 (slot-descriptions defs)
   	 (slot-storage (allocate-slot-storage (length slot-descriptions)
   					      *secret-unbound-value*))
  
positive.code: ;; 		 :datum new-class)
  ;; 	  (setf (gethash name *classes*) new-class))))
  
  ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
  ;;;
  ;;; We follow the AMOP and define functions to allocate
  ;;; class instances and slot storage.  For now, these
  ;;; functions create other Common Lisp objects such as 
  ;;; structures and arrays.  In a real implementation, 
  ;;; these functions might use lower-level mechanisms
  ;;; to allocate these entities.
  
  (defstruct standard-instance class slots)
  
  (defun allocate-standard-instance (class slot-storage)
    (make-standard-instance :class class
  			  :slots slot-storage))
  
  (defun allocate-slot-storage (size initial-value)
    (make-array size :initial-element initial-value))
  
  (defun slot-contents (slot-storage location)
    (aref slot-storage location))
  
  (defun (setf slot-contents) (new-value slot-storage location)
    (setf (aref slot-storage location) new-value))
  
  ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
  ;;;
  
negative.code: 
  (defclass standard-effective-slot-definition
      (standard-slot-definition effective-slot-definition)
    #.(find-direct-slots 'standard-effective-slot-definition))
  
  (defclass specializer (metaobject)
    #.(find-direct-slots 'specializer))
  
  (defclass eql-specializer (specializer)
    #.(find-direct-slots 'eql-specializer))
  
  (defclass class (specializer)
    #.(find-direct-slots 'class))
  
  (defclass built-in-class (class)
    #.(find-direct-slots 'built-in-class))
  
  (defclass forward-reference-class (class)
    #.(find-direct-slots 'forward-reference-class))
  
  ;;; We can not use DEFCLASS to create the class named STANDARD-CLASS,
  ;;; because we already created it in order to make it posible to
  