(** 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 tsp_exists : forall A B C P, ~ Coplanar A B C P -> exists Q, TSP A B C P Q.