(** This lemma used to be an axiom in previous versions of Tarski's axiom system. It is a been shown to a theorem by Gupta in his Phd 1965. *)
(** This corresponds to l9_6 in Tarski's book. *)

Lemma col_one_side_out : forall A B X Y,
Col A X Y ->
OS A B X Y ->
Out A X Y.