1. Akers, D. (1986).International Journal of Theoretical Physics,25, 1281.
2. Amaldi, E. (1968). InOld and New Problems in Elementary Particles, G. Puppi, ed., Academic Press, New York.
3. Barut, A. O. (1971a).Journal of Mathematical Physics,12, 841.
4. Barut, A. O. (1971b). InTopics in Modern Physics, W. E. Brittin and H. Odabasi, eds., Colorado Associated University Press, Boulder, Colorado.
5. Dirac, P. A. M. (1931).Proceedings of the Royal Society A,133, 60.