proposition: Lemma maxnormal_sub A B C : maxnormal A B C -> A \subset B.
proof: Proof. by move=> maxA; rewrite proper_sub //; apply: (maxnormal_proper maxA). Qed.
imports: mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq path) mathcomp(fintype bigop finset fingroup morphism) mathcomp(automorphism quotient action commutator center)