(** Prop 7   **)

Lemma cong2_cop2_onc3__eq : forall O P X A B C, A <> B -> A <> C -> B <> C ->
OnCircle A O P -> OnCircle B O P -> OnCircle C O P -> Coplanar A B C O ->
Cong X A X B -> Cong X A X C -> Coplanar A B C X ->
X = O.