(** 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 one_or_two_sides_aux : forall A B C D X,
~ Col C A B -> ~ Col D A B -> Col A C X -> Col B D X ->
TS A B C D \/ OS A B C D.