proposition: Lemma out2__bet : forall A B C, Out A B C -> Out C A B -> Bet A B C.
proof: Proof. intros A B C Hout1 Hout2. apply l6_4_1 in Hout2. destruct Hout2 as [_ Hout2]. destruct Hout1 as [_ [_ [|]]]. assumption. exfalso. apply Hout2. assumption. Qed.
imports: GeoCoq.Tarski_dev.Ch05_bet_le