(** 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 bet_cop__tsp : forall A B C X Y P,
~ Coplanar A B C X -> P <> Y -> Coplanar A B C P -> Bet X P Y ->
TSP A B C X Y.