proposition: Lemma l4_3_1 : forall A B C A' B' C', Bet A B C -> Bet A' B' C' -> Cong A B A' B' -> Cong A C A' C' -> Cong B C B' C'.
proof: Proof. intros. apply cong_commutativity. eapply l4_3;eBetween;Cong. Qed.
imports: GeoCoq.Tarski_dev.Ch03_bet GeoCoq.Tarski_dev.Tactics.CongR