(** CongA preserves gHalfA *)

Lemma conga2_ghalfa__ghalfa : forall A B C A' B' C' D E F D' E' F',
CongA A B C D E F -> CongA A' B' C' D' E' F' -> gHalfA A B C A' B' C' ->
gHalfA D E F D' E' F'.