1. Superstring Theory Cambridge U.P.;Green,1987
2. M. Douglas and S. Shenker, Rutgers preprint RU-89-34
3. Nonperturbative two-dimensional quantum gravity
4. E. Brezin and V. Kazakov, Ecole Normale preprint.
5. D.J. Gross and N. Miljkovic, Princeton preprint PUPT 1160