1. J.D. Bjorken: Unification of elementary forces and gravitation, p. 701. London: Hardwood Academic Publishers 1978 Proc. of the 13th Rencontre de Moriond, ed. Tran Thanh Van, pp. 191. Phys. Rev. D19, 335 (1979)
2. P.Q. Hung, J.J. Sakurai: Nucl. Phys. B143, 81 (1978)
3. S.L. Glashow: Nucl. Phys.22, 579 (1961)
4. S. Weinberg: Phys. Rev. Lett.19, 1264 (1967)
5. A. Salam: Elementary particle theory, ed. N. Svartholm. Stockholm: Almquist and Wiksell 1968