1. See for instance the review talk ofJ. D. Jackson:Proceedings of the Lund International Conference on Elementary Particle Physics, (Lund, 1969), p. 63.
2. P. G. O. Freund:Phys. Rev. Lett.,20, 235 (1968);H. Harari:Phys. Rev. Lett.,30, 1395 (1968).
3. R. J. Glauber: inLectures in Theoretical Physics, Vol.1, edited byW. E. Brittin (New York, 1959), p. 315;M. M. Islam: inLectures in Theoretical Physics, Vol.9 B (New York, 1967).
4. H. W. Lewis, J. R. Oppenheimer andS. A. Wouthuysen:Phys. Rev.,73, 127 (1948);Z. Chylinski:Nucl. Phys.,44, 58 (1963);A. Białas andT. Ruijgrok:Nuovo Cimento,39, 1061 (1965).
5. M. G. Gundzik:Phys. Rev.,184, 1537 (1969).