proposition: Lemma maxainv_proper : maxainv K N -> N \proper K.
proof: Proof. by move/maxgroupp; case/andP; rewrite properE; move/normal_sub->; case/andP. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq path) mathcomp(choice fintype bigop finset fingroup morphism) mathcomp(automorphism quotient action gseries)