(** This is equivalent to the out predicate of Tarski. *)

Lemma axiom_hcong_4_uniqueness :
forall A B C O P X Y Y', ~ Col_H P O X  -> ~ Col_H A B C -> CongA A B C X O Y -> CongA A B C X O Y' ->
same_side' P Y O X -> same_side' P Y' O X -> outH O Y Y'.