  The gauge invariance of some massless Yang-Mills models can be proved for a
large class of groups using Polchinski flow equations approach. In this paper
we provide an alternative proof based on the causal approach. The proof is
purely algebraic and is based on the analysis of the anomalies. More precisely,
one can prove that the anomalies are verifying some consistency equations of
Wess-Zumino type. In the massless SU(2) Yang-Mills case, this is enough to
prove that they are absent. The same is true for QED.
