anchor.diff:      (setf (buffer-keep-binfo buffer) nil)
       (setf (buffer-nlines buffer) 1)
       (setf (buffer-undo-size buffer) 0)
  -    (setf (buffer-undo-stack buffer)
  -          (if (buffer-enable-undo-p buffer)
  -              (queue:make-queue *undo-limit*)
  -              nil))
  +    (setf (buffer-undo-stack buffer) nil)
       (setf (buffer-redo-stack buffer) nil)
       (setf (buffer-undo-node buffer) 0)
       (setf (buffer-saved-node buffer) 0)
  
positive.code:     (setf (buffer-modified-p buffer) nil)))
  
  (defun buffer-undo-1 (buffer)
    (let ((elt (queue:pop (buffer-undo-stack buffer))))
      (when elt
        (let ((*undo-mode* :undo))
          (unless (eq elt :separator)
  
negative.code:           (buffer-filename buffer)))
  
  (defun buffer-enable-undo (buffer)
    (setf (buffer-enable-undo-p buffer) t)
    nil)
  
  (defun buffer-disable-undo (buffer)
  