1. Sato, M., Miwa, T., Jimbo, M.: Holonomic quantum fields I?V. Publ. RIMS, Kyoto Univ. I-14, 223?267 (1978); II-15, 201?278 (1979); III-15, 577?629 (1979); IV-15, 871?972 (1979); V-16, 531?584 (1980)
2. Zamolodchikov, Al.B.: Two-dimensional conformal symmetry and critical four-spin correlation functions in the Ashkin-Teller model. Zh. Eksp. Teor. Fiz.90, 1808?1818 (1986)
3. Zamoldochikov, Al.B.: Many-point correlation functions in the critical Ashkin-Teller model and the free scalar field on a hyperelliptic curve. Moscow preprint, May, 1986
4. Lect. Notes in Mathematics;J.D. Fay,1973
5. Alvarez-Gaumé, L., Moore, G., Vafa, C.: Theta functions, modular invariance and strings. Commun. Math. Phys.106, 1?40 (1986)