(** * Proposition 27 If a straight line falling on two straight lines make the alternate angles equal to one another, the straight lines will be parallel to one another. *)
(** # <div style="width:748px;height:397px;display:block" id="applet_container27"></div> # **)

Lemma prop_27 : forall A D E F, TS E F A D -> CongA A E F D F E -> Par E A F D.