anchor.diff:  
   (defun push-undo-stack (buffer elt)
     (cond ((<= *undo-limit* (buffer-undo-size buffer))
  -         (tlist-rem-left (buffer-undo-stack buffer)))
  +         )
           (t
            (incf (buffer-undo-size buffer))))
     (when-interrupted-flag 
      undo
  -   (tlist-add-right (buffer-undo-stack buffer) :undo-separator))
  -  (tlist-add-right (buffer-undo-stack buffer) elt))
  +   (push :undo-separator (buffer-undo-stack buffer)))
  +  (push elt (buffer-undo-stack buffer)))
   
   (defun push-redo-stack (buffer elt)
     (push elt (buffer-redo-stack buffer)))
  
positive.code:     (setf (buffer-keep-binfo buffer) nil)
      (setf (buffer-nlines buffer) 1)
      (setf (buffer-undo-size buffer) 0)
      (setf (buffer-undo-stack buffer) (make-tlist))
      (setf (buffer-redo-stack buffer) nil)))
  
  (defun buffer-check-marked (buffer)
  
negative.code:     (setf (buffer-mark-col buffer) 0)
      (setf (buffer-nlines buffer) 1)
      (setf (buffer-undo-size buffer) 0)
      (setf (buffer-undo-stack buffer) nil)
      (setf (buffer-redo-stack buffer) nil)
      (push buffer *buffer-list*)
      buffer))
  