proposition: Lemma plg_comm2 : forall A B C D, Parallelogram A B C D -> Parallelogram B A D C.
proof: Proof. intros. induction H. left. apply plgs_comm2. assumption. right. apply plgf_comm2. assumption. Qed.
imports: GeoCoq.Tarski_dev.Ch12_parallel_inter_dec GeoCoq.Tarski_dev.Annexes.Tagged_predicates