anchor.diff:  ;;; The discriminating function does the following:
   ;;;
   ;;;   1. Compute the list of instance class numbers of the required
  -;;;      arguments that it was passed.
  +;;;      arguments that it was passed and for which the specializer
  +;;;      profile contains T.
   ;;;
   ;;;   2. Check the call history to see whether there is an entry
   ;;;      containing that list of class numbers in the CAR of the
  
positive.code: ;;; so it contains three items:
  ;;;
  ;;;   1. A list of unique number of the classes of the required
  ;;;      arguments.  The classes are the those that were passed to
  ;;;      COMPUTE-APPLICABLE-METHODS-USING-CLASSES.  This item is
  ;;;      located in the CAR of the dotted list representing the call
  ;;;      history entry.
  
negative.code:   (let* ((profile (specializer-profile generic-function))
  	 (required-argument-count (length profile))
  	 (required-arguments (subseq arguments 0 required-argument-count))
  	 (class-numbers (loop for argument in required-arguments
  			      for p in profile
  			      when p
  				collect (instance-class-number argument)))
  	 (entry (car (member class-numbers (call-history generic-function)
  			     :key #'car :test #'equal))))
      (unless (null entry)
  