In section 3.2 of Kontsevich's very interesting paper "Notes on motives in finite characteristic,", he gives an axiomatic definition of a "lattice model" attached to a Boltzmann datum (V_1,V_2,R), where V_1 and V_2 are vector spaces and R is a linear endomorphism of V_1 tensor V_2. He remarks that the 2-dimensional Ising model is an example. Can someone explain to me what V_1, V_2, and R are for the 2-dimensional Ising model?