proposition: Lemma commgV : [~ x, y^-1] = [~ x, y]^-1.
proof: Proof. by rewrite -invg_comm commVg -(invg_comm x y) ?invgK. Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat fintype) mathcomp(bigop finset binomial fingroup morphism) mathcomp(automorphism quotient gfunctor)