(** If doubling two angles makes the same result, then they are either congruent or supplementary *)

Lemma bet_suma2__or_conga : forall A B C D E F A' B' C' A0, A0 <> B ->
Bet A B A0 -> SumA A B C A B C D E F -> SumA A' B' C' A' B' C' D E F ->
CongA A B C A' B' C' \/ CongA A0 B C A' B' C'.