1. For a discussion of weak interactions, see R. E. Marshak, Riazuddin, and C. Ryan, Theory of Weak Interactions in Particle Physics, Wiley, New York, 1969;
2. E. D. Commins, Weak Interactions, McGraw-Hill, New York, 1973;
3. J. J. Sakurai, Currents and Mesons, University of Chicago Press, Chicago, 1969.
4. M. Gell-Mann, Phys. Lett.
8, 214 (1964);
5. G. Zweig, CERN preprint 8182/Th. 401 (1964), reprinted in Developments in Quark Theory of Hadrons, Vol. 1, 1964–1978 (edited by S. P. Rosen and D. Lichtenberg), Hadronic Press, MA., 1980.