(** If the angle ACB is acute and inscribed in a circle of center O, then C and O lie on the same side of AB. *)

Lemma acute_cop_onc3__os : forall O P A B C, A <> B ->
OnCircle A O P -> OnCircle B O P -> OnCircle C O P -> Coplanar A B C O -> Acute A C B ->
OS A B O C.