proposition: Lemma der_char n G : G^`(n) \char G.
proof: Proof. by elim: n => [|n IHn]; rewrite ?char_refl // dergSn charR. Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat fintype) mathcomp(bigop finset binomial fingroup morphism) mathcomp(automorphism quotient gfunctor)