anchor.diff:  
             `(progn
   
  -             ;; FIXME: How much here may need to be wrapped in EVAL-WHEN?
  -
  -             ;; NB: This macro, in effect, prevents any usage of forward
  -             ;; referenced classes in the SUPERCLASSES list
  -
  -             ;; AS SUCH, MACROLET might be useful within this
  -             ;; macroexpansion - to ensure that an appropriate direct
  -             ;; superclasses list can be computed, consistently,
  -             ;; for each of the ,%PROTO-NAME and ,%NAME classes
  -             ;;
  -             ;; Note that as this already requires that none of the
  -             ;; SUPERCLASSES will be a FORWARD-REFERENCED-CLASS,
  -             ;; it can therefore be determined - reliably - whether any
  -             ;; of a SINGLETON or PROTOTYPE-CLASS metaclass is denoted
  -             ;; in the SUPERCLASSES list for - respectively - the ,NAME
  -             ;; and ,%PROTO-NAME classes
  -
  +             ;; NB: This implementation, in effect, prevents any usage
  +             ;; of forward-referenced classes in the SUPERCLASSES list
   
                (defclass ,%proto-name (,@user-metaclass prototype-class
                                                         ,@superclasses)
  
positive.code:                                                  &allow-other-keys)
    ;; ensure that any call to MAKE-INSTANCE of a SINGLETON will produce
    ;; an object that is a subtype of the original SINGLETON
    ;;
    ;; [FIXME DNW IN SOME POST-HOC APPLICATIONS - NEEDS FURTHER TESTING]
  
    ;; NB: This may be "Early enough" to catch where PCL is initially
    ;; setting the direct-superclasses list for a class definition.
    ;;
    ;; Note that PCL may be (perhaps cheaply) setting the STANDARD-OBJECT
    ;; class into the list of DIRECT-SUPRECLASSES whenever the
    ;; direct-superclasses list is NIL in the initial DEFCLASS form.
    ;;
    ;; Theoretically. that can be removed during ENSURE-TGT-SUPERCLASS below.
    ;; [FIXME / QA]
  
    (let ((tgt-class (find-class 'singleton))
          (unused-class (find-class 'standard-object))
  
negative.code: 
  ;; --
  
  ;; FIXME: Test DEFSINGLETON with a SINGLETON superclass of a direct
  ;; superclass not repreenting a SINGLETON
  
  (eval-when ()
  
  