proposition: Lemma plg_mid_2 : forall A B C D I, Parallelogram A B C D -> Midpoint I A C -> Midpoint I B D.
proof: Proof. intros. elim (plg_mid A B C D). intros I' HI'. spliter. treat_equalities. assumption. assumption. Qed.
imports: GeoCoq.Tarski_dev.Ch12_parallel_inter_dec GeoCoq.Tarski_dev.Annexes.Tagged_predicates