Anomalous Commutators and the Box Diagram

In continuation of previous investigations, commutator anomalies associated with the box diagram are exhibited. It is found that $q$-number Schwinger terms are present in the general case for commutators of currents which are bilinear in fermion fields. Nevertheless, the Weinberg sum rule is not violated. A $c$-number Schwinger term, which involves three derivatives of a $\delta$ function, is also found.