  We study the trace and chiral anomalies of Weyl fermions in a non-abelian
gauge background in four dimensions. Using a Pauli-Villars regularization we
identify the trace anomaly, proving that it can be cast in a gauge invariant
form, even in the presence of the non-abelian chiral anomaly, that we rederive
to check the consistency of our methods. In particular, we find that the trace
anomaly does not contain any parity-odd topological contribution, whose
presence has been debated in the recent literature.
