(** * Proposition 9 To bisect a given rectilineal angle. *)
(** # <div style="width:748px;height:397px;display:block" id="applet_container9"></div> # **)

(* Specifications: *)
Lemma prop_9 : forall A B C, A <> B -> A <> C ->
exists F, InAngle F B A C /\ CongA F A B F A C.