(** 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 ncop_distincts : forall A B C D, ~ Coplanar A B C D ->
A <> B /\ A <> C /\ A <> D /\ B <> C /\ B <> D /\ C <> D.