ng substituents or a heterocyclic group optionally having substituents; and R4f is a hydrogen atom or a hydrocarbon group optionally having substituents, or a salt thereof. [31] The agent of [30], wherein the compound (If???) is an optionally N-oxidized compound represented by the formula: wherein R1g is a hydrogen atom, a hydrocarbon group optionally having substituents, a heterocyclic group opti