(** 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_cop2__eq : forall A B C U V P Q, ~ Coplanar A B C U -> U <> V ->
Coplanar A B C P -> Coplanar A B C Q -> Col U V P -> Col U V Q ->
P = Q.