proposition: Lemma trivg_card1 : (G :==: 1) = (#|G| == 1%N).
proof: Proof. by rewrite trivg_card_le1 eqn_leq cardG_gt0 andbT. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq choice) mathcomp(fintype div path tuple bigop prime finset)