Commuting difference operators arising from the elliptic C_2^{(1)}-face   model
  We study a pair of commuting difference operators arising from the elliptic C_2^{(1)}-face model. The operators, whose coefficients are expressed in terms of the Jacobi's elliptic theta function, act on the space of meromorphic functions on the weight space of the C_2 type simple Lie algebra. We show that the space of functions spanned by the level one characters of the affine Lie algebra sp(4,C) is invariant under the action of the difference operators. 
Koji Hasegawa, Takeshi Ikeda, Tetsuya Kikuchi