(defun four-spaces-to-tab (&optional begin end)
  "Replace four spaces with a tab in a region."
  (interactive "r")
  (save-excursion
	  (if mark-active
		  (replace-regexp "    " "\t" nil (point) (mark))
		(replace-regexp "    " "\t" nil (point-min) (point-max))
		)
	  )
  )