1. S. Weinberg:Phys. Rev. Lett.,19, 1264 (1967).
2. A. Salam:Proceedings of the Eighth Nobel Symposium (New York, N. Y., 1968).
3. See the report ofB. W. Lee to theXVI International Conference on High-Energy Physics, September 1972, NAL-THY-92.
4. S. Weinberg:Phys. Rev. D,5, 1412 (1972).
5. J. von Krogh: invited talk at theGerman Physical Society Meeting, Heidelberg, February 1973.