1. W. Heisenberg:Introduction to the Unified Field Theory of Elementary Particles (Interscience Publishers, New York, N. Y., 1966).
2. J. C. Pati andA. Salam:Phys. Rev. D,10, 276 (1974).
3. H. Georgi andS. L. Glashow:Phys. Rev. Lett.,32, 438 (1974).
4. M. L. Perl:Proceedings of 1977 SLAC Summer Institute on Particle Physics (1977), p. 171.
5. J. Kirkby:Proceedings of 1978 SLAC Swimmer Institute on Particle Physics (1978), p. 309.