proposition: Lemma commg_normal G H : [~: G, H] <| G <*> H.
proof: Proof. by rewrite /(_ <| _) commg_sub commg_norm. Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat fintype) mathcomp(bigop finset binomial fingroup morphism) mathcomp(automorphism quotient gfunctor)