1. B. A. Dubrovin, A. T. Fomenko, and S. P. Novikov,Modern Geometry: Methods and Applications, Part 1,The Geometry of Surfaces, Transformation Groups, and Fields [in Russian], Nauka, Moscow (1979); English transl., Springer, New York (1992).
2. R. Jackiw, “Liouville field theory: a two-dimensional model for gravity?” in:Quantum Theory of Gravity (S. M. Christensen, ed.), Adam Hilger, Bristol (1984), p. 403.
3. N. Seiberg, “Notes on quantum Liouville theory and quantum gravity,” in:Random Surfaces and Quantum Gravity (O. Alvarez et al., eds.), Plenum, New York (1991), p. 363.
4. E. Witten,Phys. Rev. Lett.,38, 121 (1977).
5. A. M. Polyakov,Phys. Lett. B.,103, 207 (1981).