1. See, for example, W.K.H. Panofsky, M. Phillips: Classical Electricity and Magnetism (Addison Wesley Publishing Co., Reading, MA 1959)
2. W. Thirring: Phil.Mag. 41, 1193 (1950). For a textbook representation see J. Bjorken and S. Drell: Relativistic Quantum Field Theory, Section 19.13
3. F. Low: Phys.Rev. 96, 1428 (1954)
4. M. Gell-Mann, M.L. Goldberger: Phys.Rev. 96, 1433 (1954)
5. A.M. Baldin: Nuclear Phys. 18, 310 (1960)