anchor.diff:  
   ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
   ;;;
  -;;; In the native compiler, we use a special immediate value to
  -;;; indicate that some location is unbound.  In the cross compiler, we
  -;;; use a unique CONS cell. 
  +;;; Unbound cells.
  +;;;
  +;;; We do not have a single universal bit pattern indicating that a
  +;;; cell is unbound.
  +;;; 
  +;;; In the native environment, we use a special immediate value for
  +;;; variable values and slot values.  In the cross compiler, we use a
  +;;; unique CONS cell.
   
   (cl:defvar +unbound+ (list nil))
  +
  +;;; For function entries, we use a particular function to mean that
  +;;; the function entry with a particular name is not fbound.  That
  +;;; particular function accepts an arbitrary number of arguments, and
  +;;; signals an error.  With this method, code that calls a named
  +;;; function in the normal way, does not have to check whether the
  +;;; cell contains a valid function.
  +
  +(cl:defvar +funbound+
  +  (lambda (&rest arguments)
  +    (declare (ignore arguments))
  +    ;; Fixme, do something much smarter here.
  +    (error "Attempt to call an undefined function.")))
   
   ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
   ;;;
  
positive.code: ;;;
  ;;;  * Proclaiming FTYPE, INLINE, NOTINLINE or DYNAMIC-EXTENT with
  ;;;    FUNCTION using the name.  Again, A LOCATION for the entry is
  ;;;    created, but the storage cell will be set +unbound+.  The
  ;;;    appropriate auxiliary entry is created and will refer to the
  ;;;    base entry.
  ;;;
  ;;;  * When the compiler sees a compound form with the CAR containing
  ;;;    a symbol that is not associated with an entry in the FUNCTION
  ;;;    namespace.  In this case, a LOCATION for the entry is created
  ;;;    and the storage cell of the entry is initialized to +unbound+.
  ;;;    A warning is also signaled, indicating that the function is
  ;;;    undefined.
  ;;;
  
negative.code:       (if (not (null function-entry))
  	  (progn
  	    ;; Make it unbound.
  	    (setf (car (storage (location function-entry))) +funbound+)
  	    ;; Remove any compiler macro that might be present referring
  	    ;; to this entry.
  	    (setf (compiler-macros *global-environment*)
  