anchor.diff:  (defclass class (specializer)
     ((%unique-number 
       :initform (prog1 *class-unique-number* (incf *class-unique-number*))
  -    :reader unique-number)
  +    :accessor unique-number)
      (%name 
       :initform nil
       :initarg :name 
  
positive.code: (define-built-in-class function (t) ())
  
  (defclass standard-object (t)
    (;; Every standard instance has a unique time stamp.  The next
     ;; available consecutive timestamp is given to an instance when it
     ;; is initialized or reinitialized.  Instances of a class hence get
     ;; a timestamp that is greater than that of the class, unless the
     ;; class is reinitialized after instances have been created.  To
     ;; check whether an instance needs to be updated, we simply check
     ;; the timestamp against that of its class.  This is done whenever
     ;; CLASS-OF is used on an instance, so that essentially nothing can
     ;; be done to an instance without this check being made.  It is
     ;; important that the timestamp be the first slot of the instance
     ;; so that low-level code knows where to look for it.
     (%timestamp
      :initform 0
      :accessor standard-instance-timestamp)
     ;; We keep a copy of the effective slots of the class that were
     ;; used to create an instance.  They are used when the instance
     ;; needs to be updated because the class has changed, and it may
     ;; also be used by the garbage collector for type information of
  
negative.code: ;;;
  ;;; The MOP class hierarchy. 
  
  (defconstant +class-unique-number-offset+ 0)
  (defconstant +instance-slots-offset+ 1)
  
  (define-built-in-class t () ())
  