anchor.diff:        (editor-error "cannot delete this virtual frame"))
       (let ((frame (search-previous-frame vf (virtual-frame-current vf))))
         (free-frame vf (virtual-frame-current vf))
  -      (setf (virtual-frame-current vf) frame)
  -      (map-frame (implementation) frame))
  +      (switch-current-frame vf frame))
       (setf (virtual-frame-changed vf) t)))
   
   (define-key *global-keymap* "C-z p" 'frame-multiplexer-prev)
  
positive.code:       (editor-error "it's full of frames in virtual frame"))
      (let ((frame (make-frame (current-frame))))
        (setup-frame frame (primordial-buffer))
  
        (allocate-frame vf frame)
        (setf (virtual-frame-current vf) frame)
        (map-frame (implementation) frame)
  
        (setf (virtual-frame-changed vf) t))))
  
  (define-key *global-keymap* "C-z d" 'frame-multiplexer-delete)
  
negative.code:   (let* ((vf (gethash (implementation) *virtual-frame-map*))
           (frame (search-next-frame vf (virtual-frame-current vf))))
      (when frame
        (switch-current-frame vf frame))
      (lem::change-display-size-hook)
      (setf (virtual-frame-changed vf) t)))
  
  