proposition: Lemma der_abelian n G : abelian (G^`(n) / G^`(n.+1)).
proof: Proof. by rewrite sub_der1_abelian // der_subS. Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat fintype) mathcomp(bigop finset binomial fingroup morphism) mathcomp(automorphism quotient gfunctor)