proposition: Lemma perp2__col : forall X Y Z A B, Perp X Y A B -> Perp X Z A B -> Col X Y Z.
proof: Proof. intros X Y Z A B. apply cop_perp2__col, all_coplanar. Qed.
imports: GeoCoq.Meta_theory.Dimension_axioms.upper_dim_2 GeoCoq.Tarski_dev.Ch10_line_reflexivity