anchor.diff:  (export '(current-marker
             markerp
             make-marker
  -          make-marker-current-point
             copy-marker
             delete-marker
             marker-buffer
  
positive.code:   (when pointp
      (setf (marker-point marker) point))
    t)
  
  
  ;;; 同じバッファ同士かの比較は保留
  
  (defun marker= (marker1 marker2)
    (assert (eq (marker-buffer marker1)
  
negative.code:       (buffer-add-marker buffer marker))
      marker))
  
  (defun copy-marker (marker &optional kind)
    (make-marker (marker-buffer marker)
                 (copy-list (marker-point marker))
  