(* 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 diff_bet_ex3 : forall A B C,
Bet A B C ->
exists D, A <> D /\ B <> D /\ C <> D /\ Col A B D.