(** 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_cop2__cop : forall A B C U V W,
Coplanar A B C U -> Coplanar A B C W -> Bet U V W -> Coplanar A B C V.