proposition: Lemma normsIG A B G : A \subset 'N(B) -> A :&: G \subset 'N(B :&: G).
proof: Proof. by move/normsIs->; rewrite ?normG. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq choice) mathcomp(fintype div path tuple bigop prime finset)