proposition: Lemma invg_comm x y : [~ x, y]^-1 = [~ y, x].
proof: Proof. by rewrite commgEr conjVg invMg invgK. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq choice) mathcomp(fintype div path tuple bigop prime finset)