(** If the angle ACB is obtuse and inscribed in a circle of center O, then C and O lie on opposite sides of AB. *)

Lemma cop_obtuse_onc3__ts : forall O P A B C,
OnCircle A O P -> OnCircle B O P -> OnCircle C O P -> Coplanar A B C O -> Obtuse A C B ->
TS A B O C.