anchor.diff:    (move-mark-to-mark mark (buffer-point buffer)))
   
   (defun mark-at-point-p (buffer mark)
  -  (mark-equal-p mark (buffer-point buffer)))
  +  (mark= mark (buffer-point buffer)))
   
   (defun start-of-line-p (mark)
     (eql (mark-charpos mark) 0))
  
positive.code: 
  (defun editor-loop ()
    (loop
       (handler-case
           (let* ((*this-character* (editor-read-char))
                  (*this-command* (translate-command *editor* *this-character*)))
             (cond (*this-command*
                    (funcall *this-command*))
                   (t (format t "Unknown command ~S~%" *this-character*)))
             (setf *last-command* *this-command*)
             (setf *last-character* *this-character*)
             (setf (pending-redisplay *editor*) (not (redisplay))))
         (error (c)
           (ignore-errors
             (format t "Editor error: ~A~%" c))))))
  
  (defun initialize-global-key-map (editor)
    (let ((global-key-map (global-key-map editor)))
      (clrhash global-key-map)
      (flet ((set-key (key fn)
               (setf (gethash key global-key-map) fn)))
        (set-key #\Newline 'self-insert-command)
        ;; ASCII printable characters.
        (loop for i from #x20 to #x7E
           do (set-key (code-char i) 'self-insert-command))
        ;; Latin 1 printable characters.
        (loop for i from #xA0 to #xFF
           do (set-key (code-char i) 'self-insert-command))
        (set-key #\C-F 'forward-char-command)
        (set-key #\C-B 'backward-char-command)
        (set-key #\C-N 'next-line-command)
        (set-key #\C-P 'previous-line-command)
        (set-key #\C-A 'move-beginning-of-line-command)
        (set-key #\C-E 'move-end-of-line-command)
        (set-key #\C-K 'kill-line-command)
        (set-key #\C-Q 'quoted-insert-command)
        (set-key #\C-L 'recenter-command)
        (set-key #\M-L 'redraw-screen-command)
        (set-key #\C-Space 'set-mark-command)
        (set-key #\C-X 'exchange-point-and-mark-command)
        (set-key #\Backspace 'delete-backward-char-command)
        (set-key #\C-D 'delete-forward-char-command)
        (set-key #\Delete 'delete-forward-char-command)
        (set-key #\C-W 'kill-region-command)
        (set-key #\C-Y 'yank-command))))
  
  (defun editor-main (width height)
    (mezzanine.gui.font:with-font (font mezzanine.gui.font:*default-monospace-font* mezzanine.gui.font:*default-monospace-font-size*)
  
negative.code:                   (buffer-property buffer 'pane-previous-mark-position) previous-mark-position))
            ;; If the point has moved, then invalidate the line that contained the point and the line that
            ;; now holds the point.
            (when (not (mark= point previous-point-position))
              (flush-display-line previous-point-position)
              (flush-display-line point))
            ;; If the mark changes state, flush lines within the region.
  