proposition: Lemma trivg_card_le1 : (G :==: 1) = (#|G| <= 1).
proof: Proof. by rewrite eq_sym eqEcard cards1 sub1G. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq choice) mathcomp(fintype div path tuple bigop prime finset)