proposition: Lemma cong2_per2__cong_3 : forall A B C A' B' C', Per A B C -> Per A' B' C' -> Cong A C A' C' -> Cong B C B' C' -> Cong_3 A B C A' B' C'.
proof: Proof. intros. unfold Cong_3. assert (Cong B A B' A') by (apply (cong2_per2__cong A B C A' B' C');auto). repeat split;Cong. Qed.
imports: GeoCoq.Tarski_dev.Ch10_line_reflexivity_2