1. Selected papers can be found in: J. Schwarz (ed.): Super strings. Singapore: World Scientific 1985
2. M. Green, J. Schwarz: Phys. Lett.149B, 119 (1984)
3. D. Gross, J. Harvey, E. Martinec, R. Rohm: Phys. Rev. Lett.54, 502 (1985); Nucl. Phys.B256, 253 (1985); Nucl. Phys.B267, 75 (1986)
4. J. Ellis, K. Enqvist, D.V. Nanopoulos, F. Zwirner: Nucl. Phys.B276, 14 (1986)
5. Th. Kaluza: Sitzungsber. Preuss. Akad. Wiss., Berlin, Math. Phys.K1, 966 (1921); O. Klein: Z. Phys.37, 895 (1926); E. Witten: Nucl. Phys.B186, 412 (1981), and references therein