proposition: Lemma lemma_congruencesymmetric : forall A B C D, Cong B C A D -> Cong A D B C.
proof: Proof. intros. assert (Cong B C B C) by (conclude cn_congruencereflexive). assert (Cong A D B C) by (conclude cn_congruencetransitive). close. Qed.
imports: GeoCoq.Elements.OriginalProofs.euclidean_tactics