Derivative expansions of fermion-number currents

It is shown, by constructing an appropriate homotopy operator on differential forms, that the derivative expansion of a conserved fermion-number current can be written term-by-term as a total divergence, apart from the leading gauged topological term. As a corollary, it is shown that the derivative expansion of the effective action for massive chiral fermions is local and chiral gauge invariant, apart from the gauged Wess-Zumino term which produces the chiral anomaly.