(* # P11 (*) Modified run-length encoding. *)
(* #  *)
(* # Modify the result of problem P10 in such a way that if an element has no *)
(* # duplicates it is simply copied into the result list. Only elements with *)
(* # duplicates are transferred as (N E) lists. *)
(* #  *)
(* # Example: *)
(* # * (encode-modified '(a a a a b c c a a d e e e e)) *)
(* # ((4 A) B (2 C) (2 A) D (4 E)) *)