(** * Proposition 16 In any triangle, if one of the sides is produced, the exterior angle is greater than either of the interior and opposite angles. *)
(** # <div style="width:748px;height:397px;display:block" id="applet_container16"></div> # **)

Lemma prop_16 : forall A B C D, ~ Col A B C -> Bet B C D -> C <> D ->
LtA C A B A C D /\ LtA C B A A C D.