CFTs are naturally defined on Riemann surfaces. The rational ones can be
solved using methods from algebraic geometry. One particular feature is the
covariance of the partition function under the mapping class group. In genus
g=1, this yields modular forms, which can be linked to ordinary differential
equations of hypergeometric type with algebraic solutions.Comment: 30 pages. Revised and extended version. (The paper was originally
part of arXiv:1305.0469, which had been split into the present paper and
arXiv:1705.07627.