anchor.diff:  				    (eq (pane-display-time pane) :command-loop)
   				    (pane-display-function pane))
   			       (let ((func (pane-display-function pane)))
  -				 (window-clear pane)
  -				 (funcall func frame pane))))
  +				 (window-erase-viewport pane)
  +				 (funcall func frame pane) ; XXX other arguments
  +                                        ; XXX incremental redisplay
  +                                 )))
   		       (frame-top-level-sheet frame))
         (when *standard-input*
   	(setf (cursor-visibility (stream-text-cursor *standard-input*)) t)
  
positive.code: 	    (if (stringp prompt)
  		(write-string prompt *standard-input*)
  	      (funcall prompt *standard-input* frame))
  	    (finish-output *standard-input*)))	  
  	(let ((command (read-frame-command frame)))
  	  (fresh-line *standard-input*)
  	  (when command
  
negative.code: 
  (defun find-pane-of-type (panes type)
    (find-pane-if #'(lambda (pane) (typep pane type)) panes))
  
  (defmethod frame-current-panes ((frame application-frame))
    (find-pane-if #'(lambda (pane) (pane-name pane))
                  (frame-current-layout frame)))
  