proposition: Lemma plg_cong : forall A B C D, Parallelogram A B C D -> Cong A B C D /\ Cong A D B C.
proof: Proof. intros. induction H. apply plgs_cong. assumption. apply plgf_cong. assumption. Qed.
imports: GeoCoq.Tarski_dev.Ch12_parallel_inter_dec GeoCoq.Tarski_dev.Annexes.Tagged_predicates