1. J. M. Jauch. Phys. Rev. 63, 334 (1943), does obtain a finite value but it seems to us that he has discussed only one of many terms.
2. E. C. G. Stueckelberg, Helv. Phys. Acta 17. 3 (1944); ibid. 18, 3 (1945).
3. E. C. G. Stueckelberg, Helv. Phys. Acta 19, 242 (1946); Phys. Soc. Cambridge Conference Report 199 (1947).
4. Wentzel, Helv. Phys. Acta 21, 49 (1948).