1. W. v. Ignatowsky:Phys. Zeits.,21, 972 (1910);P. Frank andH. Rothe:Ann. der Phys.,34, 825 (1911);E. Hahn:Arch. Math. Phys.,21, 1 (1913);F. Severi: inCinquant’anni di relatività, edited byM. Pantaleo (Firenze, 1955);M. Camenzind:General Relat. Gravit.,1, 71 (1970);V. Berzi andV. Gorini:Journ. Math. Phys.,10, 1518 (1969);V. Gorini andA. Zecca:Journ. Math. Phys.,11, 2226 (1970);A. Agodi: unpublished (1973).
2. E. Recami andR. Mignani:Riv. Nuovo Cimento,4, 209 (1974);R. Mignani andE. Recami:Int. Journ. Theor. Phys. (to appear).
3. The «third postulate» is known also as «reinterpretation principle» (RIP). See ref. (2), andP. A. M. Dirac:Proc. Roy. Soc., A126, 360 (1930);E. C. G. Stückelberg:Helv. Phys. Acta,14, 32L, 588 (1941);R. P. Feynman:Phys. Rev.,76, 749, 769 (1949);O. M. P. Bilaniuk, V. K. Deshpande andE. C. G. Sudarshan:Amer. Journ. Phys.,30, 718 (1962);S. Weinberg:Gravitation and Cosmology (New York, N. Y., 1972).
4. Notice that, in relativity, all events of the Minkowski space should bea priori considered as «always existing». Cf.,e.g.,G. Arcidiacono:Relatività e cosmologia (Roma, 1973).
5. In this work the word «charge» is used in itswidest meaning to indicate any possible «additive charge». Cf. ref. (2).