anchor.diff:                           ;; set action when click
                            (let ((frame frame))
                              (lambda ()
  -                             (setf (virtual-frame-current window) frame)
  -                             (setf (virtual-frame-changed window) t)))
  +                             (switch-current-frame virtual-frame frame)))
                            :attribute (if focusp
                                           'frame-multiplexer-active-frame-name-attribute
                                           'frame-multiplexer-frame-name-attribute))
  
positive.code:       (editor-error "cannot delete this virtual frame"))
      (let ((frame (search-previous-frame vf (virtual-frame-current vf))))
        (free-frame vf (virtual-frame-current vf))
        (switch-current-frame vf frame))
      (setf (virtual-frame-changed vf) t)))
  
  (define-key *global-keymap* "C-z p" 'frame-multiplexer-prev)
  (define-command frame-multiplexer-prev () ()
  
negative.code: 
  (defun switch-current-frame (virtual-frame frame)
    (setf (virtual-frame-current virtual-frame) frame)
    (setf (virtual-frame-changed virtual-frame) t)
    (map-frame (implementation) frame))
  
  (defun find-unused-frame-id (virtual-frame)
  