(** 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 ts2__inangle : forall A B C P, TS A C B P -> TS B P A C ->
InAngle P A B C.