1. Cf.S. L. Adler andR. F. Dashen:Current Algebras (New York, N. Y., 1968), p. 15.
2. P. G. Federbush andM. T. Grisaru:Nuovo Cimento,9, 890 (1958).
3. Some authors, cf.J. Bernstein:Elementary Particles and Their Currents (San Francisco, Cal., 1968), p. 12, state that the discrete conserved quantities cannot be related to currents. However, if one expands the usual definition of a current to include not only four-vector currents but also nonlocal tensor currents, then (as we shall show) a conserved current in this sense can be constructed.
4. Cf.J. D. Bjorken andS. D. Drell:Relativistic Quantum Fields (New York, N. Y., 1965), p. 111.
5. D. M. Fradkin:Journ. Math. Phys.,6, 880 (1965).