proposition: Lemma ncol123_plg__plgs : forall A B C D, ~ Col A B C -> Parallelogram A B C D -> Parallelogram_strict A B C D.
proof: Proof. intros A B C D HNC H; induction H; auto. exfalso; apply HNC; unfold Parallelogram_flat in *; spliter; Col. Qed.
imports: GeoCoq.Tarski_dev.Ch12_parallel_inter_dec GeoCoq.Tarski_dev.Annexes.Tagged_predicates