(** 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 col2_cop__cop : forall A B C D E F, Coplanar A B C D -> C <> D -> Col C D E -> Col C D F ->
Coplanar A B E F.