1. T. Kaluza:Sitzungsber. Preuss. Akad. Wiss. Phys. Math. Kl., 966 (1921);
2. O. Klein:Z. Phys.,37, 895 (1926);
3. Y. K. Cho andP. A. O. Freund:Phys. Rev. D,12, 1711 (1975).
4. H. Saller: preprint MPI-PAE/PTh 7/83 (January 1983).
5. H. P. Dürr:Properties of Matter under Unusual Conditions, edited byH.Mark andS. Feshbach (New York, N.Y., 1969).