1. A. Pais andG. E. Uhlenbeck:Phys. Rev.,79, 145 (1950);M. Born:Rev. Mod. Phys.,21, 463 (1949);S. Fubini: inProceedings of the XVII International Conference on High-Energy Physics (London, 1974).
2. W. Heitler: inThe Quantum Theory of Fields, edited byR. Stoops (New York, N. Y., 1962);R. P. Feynman:Theory of Fundamental Processes (New York, N. Y., 1962), p. 139;N. Nakanishi:Suppl. Prog. Theor. Phys.,51, 1 (1972).
3. J. P. Hsu:Lett. Nuovo Cimento,19, 655 (1977). See alsoFound. Phys.,8, 371 (1978), appendix p. 388–390.
4. E. C. G. Sudarshan:Fields and Quanta,2, 175 (1972);M. E. Arons, M. Y. Han andE. C. G. Sudarshan:Phys. Rev.,137, B 1085 (1965).
5. T. D. Lee andG. C. Wick:Phys. Rev. D,2, 1033 (1970).