(** * Proposition 23 On a given straight line and at a point on it to construct a rectilineal angle equal to a given rectilineal angle. *)
(** # <div style="width:748px;height:397px;display:block" id="applet_container23"></div> # **)

(* Specifications: *)
Lemma prop_23 : forall A B C D E, A <> B -> C <> D -> C <> E ->
exists F, CongA D C E B A F.