1. Gepner, D.: Nucl. Phys. B296, 757 (1988); Phys. Lett.199 B, 380 (1987)
2. Gepner, D., Witten, E.: Nucl. Phys. B278, 493 (1986)
3. Gepner, D.: Nucl. Phys. B290, FS20, (1) 10 (1987)
4. Kac, V.G.: Infinite dimensional Lie algebras. Cambridge: Cambridge University Press 1985
5. Gepner, D.: Lectures onN=2 string theory. In the Proceedings of the Trieste Spring School, 3–14 April 1989. Green, M. et al. (ed.). Singapore: World Scientific 1990