proposition: Lemma between_cong_2 : forall A B D E, Bet A D B -> Bet A E B -> Cong A D A E -> D = E.
proof: Proof. intros. apply cong3_bet_eq with A B; unfold Cong_3; repeat split; Cong. eapply (l4_2 B E A B B D A B). unfold IFSC; repeat split; Cong; Between. Qed.
imports: GeoCoq.Tarski_dev.Ch04_col