(** The sum of two angles is equal to the sum of their two supplementary angles *)

Lemma suma_suppa2__suma : forall A B C D E F G H I A' B' C' D' E' F',
SuppA A B C A' B' C' -> SuppA D E F D' E' F' -> SumA A B C D E F G H I ->
SumA A' B' C' D' E' F' G H I.