(* Lemma t2_8 : forall A B C D E : Tpoint, Bet A B C -> Bet D B E -> Cong A B D B -> Cong B C B E -> Cong A E C D. *)

Lemma bet2__out : forall A B C B', A <> B -> A <> B' -> Bet A B C -> Bet A B' C -> Out A B B'.