(** In a right triangle, the midpoint of the hypotenuse is the circumcenter. *)

(* Specifications: *)
Lemma thales_converse_theorem : forall A B C M, A <> C -> B <> C ->
Midpoint M A B -> Per A C B -> Cong M A M C.
Lemma bet_cong__ghalfa : forall A B C B', A <> B -> B <> C -> A <> B' ->
Bet B A B' -> Cong A B A C -> gHalfA A B C C A B'.