(** * Proposition 5 In isosceles triangles the angles at the base are equal to one another, and, if the equal straight lines be produced further, the angles under the base will be equal to one another. *)
(** # <div style="width:748px;height:397px;display:block" id="applet_container5"></div> # **)

(* Specifications: *)
Lemma prop_5_1 : forall A B C, A <> B -> B <> C -> Cong A B A C -> CongA A B C A C B.
Lemma prop_5_2 : forall A B C F G, A <> B -> B <> C -> Cong A B A C ->
Bet A B F -> B <> F -> Bet A C G -> C <> G ->
CongA F B C G C B.