1. R. Feynman and M. Gell-Mann, Phys. Rev. 109, 193 (1958).
2. R. Marshak and G. Sudarshan, Padua-Venice International Conference, 1957; Phys. Rev. 109, 1860 (1958). J. J. Sakurai, Nuovo Cimento 7, 649 (1958).
3. N. Cabibbo, Phys. Rev. Letters 10, 513 (1963).
4. The references for the various selection rules are quite numerous. We give only a partial list of the theoretical papers. For the ΔS ≦ 1 rule, see L. B. Okun and B.M. Pontecorvo, J. Exp. Theor. Phys. (U.S.S.R.) 32, 1587 (1957) [translation, Soviet Phys. J.E.T.P. 5, 1297 (1957)]. For the ΔQh = ΔS rule and the iso-triplet hypothesis of the vector current, see R. Feynman and M. Gell-Mann (reference 1). For the Δ I = 1 1/2 rule, see M. Gell-Mann and A. Pais, Proceedings of the International Conference on High Energy Physics, Pergamon Press, London (1955)
5. R. Marshak, S. Okubo, E. C. G. Sudarshan, W. B. Teutsch and S. Weinberg, Phys. Rev. 112, 665 (1958). For the Δ I = 1 rule see T. D. Lee and C. N. Yang, Phys. Rev. 126, 2239 (1962). For the SU3 transformation properties of the weak interaction see N. Cabibbo (reference 3).