1. H. B. Thacker, C. Quigg andJ. L. Bosner:Phys. Rev. D,18, 274, 287 (1978);H. Grose andA. Martin:Nucl. Phys. B,148, 413 (1979).
2. K. Gottfried:Proceedings of the International Symposium on Lepton and Photon Interactions at High Energy, edited byF. Gutbrod (Hamburg, 1977), p. 667.
3. C. Quigg andJ. L. Rosnee: Fermilab preprint 80/13-THY (1981).
4. R.Van Royen andV. F. Weiskopf;Nuovo Cimento A,50, 617 (1967);51, 583 (1967).
5. J. M. Jauch andF. Rohrlich:The Theory of Photons and Electrons, 2nd edition (Berlin, 1980), chapt. 12.