anchor.diff:                       store-syms
                        expansion
                        `(,access-fn ,@param-syms)))))
  -    (setf (get access-fn 'setf-expander) #'expand
  -          (get access-fn 'setf-update-fn) nil))
  +    (setf (get access-fn 'setf-expander) #'expand))
     access-fn)
   )
   
  
positive.code: 
  (eval-when (:compile-toplevel :load-toplevel :execute)
  (defun %define-setf-expander (access-fn expander)
    (setf (get access-fn 'setf-expander) expander
          (get access-fn 'setf-update-fn) nil))
  )
  
  (define-modify-macro incf (&optional (delta 1)) +)
  
negative.code:       (setf (first results) 'psetf)
        `(progn ,results 'nil))))
  
  (defmacro defsetf (access-fn &rest args)
    (cond ((listp (first args))
           `(defsetf-long ,access-fn ,@args))
  