(** 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_two_sides : forall A B C P Q,
Col A B C -> A <> C -> TS A B P Q ->
TS A C P Q.