1. H. R. Lehmann andR. A. Treumann:Phys. Lett. A,45, 215 (1973).
2. E. Recami: inM. Pantaleo andF. De Finis:Albert Einstein 1879–1979, Relativity, Quanta and Cosmology, Vol. II (Johnson Reprint Corporation, New York, N. Y., 1979), and many references therein.
3. H. C. Corben:Nuovo Cimento A,29, 415 (1975).
4. H. C. Corben: inE. Recami:Tachyons, Monopoles and Related Topics (North Holland, Amsterdam, 1978), p. 31.
5. St. Mrówczyśki:Lett. Nuovo Cimento,38, 247 (1983).