1. A. Connes, Pub. Math. I.H.E.S., 62, 257 (1986).
2. C.M. DeWitt and J.A. Wheeler, 1967 Lectures in Mathematics and Physics (Battelle Rencontres, Benjamin, New York, 1968).
3. M. Dresden, H.A. Kramers, Between Tradition and Revolution (Springer-Verlag, New York, 1987).
4. J.M. Jauch and F. Rohrlich, The Theory of Photons and Electrons (Addison-Wesley, Reading, Massachussets, 1955).
5. V. Kaplunovsky and M. Weinstein, Phys.Rev. D31, 1879 (1985).