anchor.diff:        (do ((res #1=(buffer-undo-1 buffer) #1#)
              (pres nil res))
             ((not res) pres))
  +    (decf (buffer-undo-node buffer))
       (push :undo-separator (buffer-redo-stack buffer))))
   
   (defun buffer-redo-1 (buffer)
  
positive.code:   (prog1 (do ((res #1=(buffer-redo-1 buffer) #1#)
                (pres nil res))
               ((not res) pres))
      (push :undo-separator (buffer-undo-stack buffer))))
  
  (defun buffer-get (buffer indicator &optional default)
  
negative.code:          (incf (buffer-undo-size buffer))))
    (when-interrupted-flag 
     :undo
     (incf (buffer-undo-node buffer))
     (push :undo-separator (buffer-undo-stack buffer)))
    (push elt (buffer-undo-stack buffer)))
  
  