proposition: Lemma orth_distincts : forall A B C U V, Orth A B C U V -> A <> B /\ B <> C /\ A <> C /\ U <> V.
proof: Proof. intros A B C U V [X HX]. apply orth_at_distincts with X, HX. Qed.
imports: GeoCoq.Tarski_dev.Ch10_line_reflexivity_2