anchor.diff:      :initarg :impl
       :initform nil
       :accessor virtual-frame-impl
  -    :type lem:implementation)
  +    :type implementation)
      (id/frame-table
       :initarg :id/frame-table
       :accessor virtual-frame-id/frame-table
  
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
  