(require 'cl-lib)
(defun index-abc (&optional beg end)
  (interactive (if (use-region-p)
                   (list (region-beginning) (region-end))
                 (list (point-min) (point-max) )))
  (save-excursion
    (save-restriction
      (narrow-to-region beg end)
      (goto-char (point-min))
      (cl-loop for i from ?A to ?Z do
               (when (re-search-forward "^" nil t)
                 (insert (char-to-string i) " ") )))))

(defun rectangle-char-lines (beg end letter)
   (interactive "r\ncStart letter:")n
   (rectangle-number-lines beg end letter "%c ") )

;; a Kate Moss
;; b Elle Macpherson
;; c Alicia Silverstone