anchor.diff:                 (line-offset (buffer-end point) (- line-number nlines)))))))
   
   (defun check-marked ()
  +  "`current-buffer`内でマークが置かれていなければ`editor-error`を起こします。"
     (unless (buffer-mark (current-buffer))
       (editor-error "Not mark in this buffer")))
   
  
positive.code:         (delete-point mark)))))
  
  (defun insert-buffer (point buffer)
    (loop :for line := (point-line (buffer-start-point buffer)) :then (line-next line)
          :while line
          :do (insert-string point (line-str line))
  
negative.code:   point)
  
  (defun blank-line-p (point)
    "`point`のある行が空白だけなら、その空白の個数、それ以外ならnilを返します。"
    (let ((string (line-string point))
          (eof-p (last-line-p point))
          (count 0))
  