1. CERN report;B Zumino,1972
2. A systematic development of source theory will be found in J. Schwinger, Particles, Sources and Fields (Addison-Wesley, Reading, Mass.), Vol.1 (1970) and Vol. II (1973).
3. It is also reviewed briefly in J. Schwinger, Phys. Rev. D 7, 908 (1973).
4. The first use of such a classification is in E. Konopinski and H. Mahmoud, Phys. Rev. 92, 1045 (1953)
5. However, the independent introduction of this concept of leptonic charge [J. Schwinger, Ann. Phys. (N.Y.) 2, 407 (1957)] owed nothing to the earlier work but was a reaction to the then new situation of parity nonconservation in which helicity had become the only discrete quantum number generally attributed to the neutrino. The denial of the latter view was the later vindicated prediction of two neutrinos