Difference equations for the correlation functions of the eight vertex   model
  We propose that the correlation functions of the inhomogeneous eight vertex model in the anti-ferroelectric regime satisfy a system of difference equations with respect to the spectral parameters. Solving the simplest difference equation we obtain the expression for the spontaneous staggered polarization conjectured by Baxter and Kelland. We discuss also a related construction of vertex operators on the lattice. 
M. Jimbo, T. Miwa, A. Nakayashiki