anchor.diff:           (frame (search-next-frame vf (virtual-frame-current vf))))
       (when frame
         (setf (virtual-frame-current vf) frame)
  -      (lem:map-frame (implementation) frame))
  +      (map-frame (implementation) frame))
       (lem::change-display-size-hook)
       (setf (virtual-frame-changed vf) t)))
   
  
positive.code:          (id (find-unused-frame-id vf)))
      (when (null id)
        (editor-error "it's full of frames in virtual frame"))
      (let ((frame (lem:make-frame (current-frame))))
        (lem:setup-frame frame (primordial-buffer))
  
        (setf (virtual-frame-current vf) frame)
        (allocate-frame vf frame)
        (lem:map-frame (implementation) frame)
  
        (setf (virtual-frame-changed vf) t))))
  
  
negative.code:   (let* ((buffer (make-buffer "*frame-multiplexer*" :enable-undo-p nil :temporary t))
           (id/frame-table (make-array +frame-multiplexer-max-number-of-frames+ :initial-element nil)))
      (setf (aref id/frame-table 0) frame)
      (setf (variable-value 'truncate-lines :buffer buffer) nil)
      (let ((vf (make-instance 'virtual-frame
                               :impl impl
                               :buffer buffer
  