proposition: Lemma der_group_set G n : group_set G^`(n).
proof: Proof. by case: n => [|n]; apply: groupP. Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat fintype) mathcomp(bigop finset binomial fingroup morphism) mathcomp(automorphism quotient gfunctor)