1. E. Cunningham andH. Bateman [Proc London Hath. Soc,8, 75 (1909);8, 223 (1910); has been widely discussed in relation to possible extended particle structure [F. Bopp:Lecture Int. Conf. Theor. Phys. (Kyoto, 1953), andR. L. Ingraham:Nuovo Cimento,9, 886 (1952): as a local group of invariance for the classical radiating electron [seeP. A. M. Dirac, ref. (20)].
2. M. Flato andD. Stebnheimeb:Compt, Rend.,260, 3532 (1965), andNucl. Phys. (tc be published). See alsoD. Böhm, M. Flato, F. Halbwachs, P. Hillion andJ. P. Vigieb:Nuovo Cimento,36, 672 (1965).
3. M. Flato, D. Sternheimer andJ. P. Vigier:Compt. Rend.,260, 3869 (1965).
4. I. E. Segal:Duke Math. Journ.,18, 221 (1951).
5. E. P. Wigner andE. Isönü:Proc. Nat. Acad. Sci.,39, 516 (1953).