1. T. Elber, Some External Field Problems in Quantum Electrodynamics (1971).
2. C. S. Chen and D. White, Phys. Rev. Lett.,28, 7, 455 (1972).
3. S. Shweber, H. Bethe, and F. Hofman, Mesons and Fields [Russian translation], IL (1957), p. 347.
4. V. B. Berestetskii, E. M. Lifshits, and L. P. Pitaevskii, Relativistic Quantum Theory [in Russian], Nauka (1968).
5. A. A. Sokolov and I. M. Ternov (editors), Synchrotron Radiation [in Russian], Nauka, Moscow (1966).