(** This is Theorem 18.17 from Martin *)

(* Specifications: *)
Lemma bet_le__lt : forall A B C D, Bet A D B -> A <> D -> D <> B -> Le A C B C -> Lt D C B C.
Lemma t18_18_aux : forall A B C D E F,
Cong A B D E -> Cong A C D F -> LtA F D E C A B -> ~ Col A B C -> ~ Col D E F -> Le D F D E ->
Lt E F B C.