1. F. E. Low:Phys. Rev.,110, 974 (1958).
2. J. M. Jauch andF. Rohrlich:The Theory of Photons and Electrons (Reading, Mass., 1955), p. 390.
3. R. H. Dalitz:Phys. Rev.,99, 915 (1955).
4. G. H. Trilling:Proc. Intern. Conf. Weak Interactions (Argonne, 1965), p. 115.
5. All the numerical calculations were performed on the IBM 7090 of Pisa University.