proposition: Lemma morphimD1 A : (f @* A)^# \subset f @* A^#.
proof: Proof. by rewrite -!set1gE -morphim1 morphimD. Qed.
imports: mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq choice) mathcomp(fintype finfun bigop finset fingroup)