proposition: Lemma normalGI G H A : H \subset G -> A <| G -> H :&: A <| H.
proof: Proof. by move=> sHG /andP[_ nAG]; apply: norm_normalI (subset_trans sHG nAG). Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq choice) mathcomp(fintype div path tuple bigop prime finset)