1. P. Minkowski, μ → eγ at a Rate of One Out of 1-Billion Muon Decays?, Phys. Lett. B 67 (1977) 421 [ SPIRES ].
2. M. Gell-Mann, P. Ramond and R. Slansky, Complex spinors and unified theories, in Sanibel Talk, CALT-68-709, Feb. 1979, and in Supergravity, North Holland, Amsterdam (1979).
3. T. Yanagida, Horizontal symmetry and masses of neutrinos, in proceedings of the Workshop on Unified Theory and Baryon Number of the Universe, KEK, Japan, 1979.
4. S.L. Glashow, Quarks and leptons, Cargese Lectures (1979).
5. R.N. Mohapatra and G. Senjanović, Neutrino mass and spontaneous parity nonconservation, Phys. Rev. Lett. 44 (1980) 912 [ SPIRES ].