proposition: Lemma plg_not_comm_2 : forall A B C D : Tpoint, A <> B -> Parallelogram A B C D -> ~ Parallelogram B A C D.
proof: Proof. intros. assert (HNC := plg_not_comm A B C D H H0); spliter; assumption. Qed.
imports: GeoCoq.Tarski_dev.Ch12_parallel_inter_dec GeoCoq.Tarski_dev.Annexes.Tagged_predicates