1. The notation is that of J. Bjorken and S. Drell, Relativistic Quantum Fields, McGraw-Hill 1965, except for a change of sign in 5.
2. H. Pietschmann, Springer Tracts in Modern Phys. 52, 193 (1970). This paper will be referred to as I.
3. T. D. Lee and C. N. Yang, Phys. Rev. 108, 1611 (1957).
4. P. Kristenson and C. Moller, Dan.Mat.Fys.Medd.27/7 (1952) .
5. See for example C. Rubbia in “The growth points in physics”, Proceedings of the EPS Conference in Florence, April 1969.