1. Constantinescu F. (1980). Distributions and their Applications in Physics. Pergamon Press, Oxford
2. Schwinger J. (1951). On gauge invariance and vacuum polarization. Phys. Rev. 82: 664
3. Aste A., Scharf G. and Walther U. (1998). Power counting degree versus singular order in the Schwinger model. Nuovo Cim. A 111: 323
4. Streater R.F. and Wightman A.S. (1964). PCT, Spin, Statistics and All That. Benjamin-Cummings Publishing Company, New York
5. Scharf G. (1995). Finite Quantum Electrodynamics. 2nd edn. Springer, New York