anchor.diff:    (setf (gf-methods generic-function)
   	(remove method (gf-methods generic-function)))
     ;; Call REMOVE-DIRECT-METHOD for each of the specializers of METHOD.
  -  (loop for specializer in (m-specializers method)
  +  (loop for specializer in (method-specializers method)
   	do (remove-direct-method specializer method))
     ;; Disassociate GENERIC-FUNCTION from METHOD.
     (setf (m-generic-function method) nil)
  
positive.code: 		     (and (null (set-exclusive-or
  				 (method-qualifiers method)
  				 (method-qualifiers existing-method)))
  			  (equal (m-specializers method)
  				 (m-specializers existing-method))))
  		   (gf-methods generic-function))))
      (unless (null method-to-remove)
        (remove-method generic-function method-to-remove)))
  
negative.code:   ;; Associate GENERIC-FUNCTION with METHOD.
    (setf (m-generic-function method) generic-function)
    ;; Call ADD-DIRECT-METHOD for each of the specializers of METHOD.
    (loop for specializer in (method-specializers method)
  	do (add-direct-method specializer method))
    ;; Call COMPUTE-DISCRIMINATING-FUNCTION and install its result
    ;; with SET-FUNCALLABLE-INSTANCE-FUNCTION. 
  