proposition: Lemma sub_mmax_proper M H : M \in 'M -> H \subset M -> H \proper G.
proof: Proof. by move=> maxM sHM; apply: sub_proper_trans (mmax_proper maxM). Qed.
imports: HB(structures) mathcomp.ssreflect.ssreflect mathcomp(ssrbool ssrfun eqtype ssrnat seq div choice fintype bigop) mathcomp(finset prime fingroup morphism automorphism action quotient) mathcomp(gfunctor cyclic pgroup center commutator gseries nilpotent) mathcomp(sylow abelian maximal hall) odd_order(BGsection1 BGsection6)