The vertex function and adiabatic limit in finite QED

The vertex function is computed in the cutoff-free causal formulation of QED. By normalization at zero momentum, difficulties with the infrared problem are avoided. The latter is studied in the course of the adiabatic limit, where the spacetime switching function goes to one. This allows the authors to keep the photon mass always equal to zero. They prove that the adiabatic limit exists in the inclusive cross section.