(** 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 ex_ncol_cop : forall A B C D E, D <> E ->
exists F, Coplanar A B C F /\ ~ Col D E F.