(** Basic properties about the sum of the angles of a triangle *)

Lemma conga3_trisuma__trisuma : forall A B C D E F A' B' C', TriSumA A B C D E F ->
CongA A B C A' B' C' -> CongA B C A B' C' A' -> CongA C A B C' A' B' ->
TriSumA A' B' C' D E F.