(** 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 out_two_sides_two_sides :
forall A B X Y P PX,
A <> PX ->
Col A B PX ->
Out PX X P ->
TS A B P Y ->
TS A B X Y.