The two-dimensional critical Ising model is the critical limit of the Ising model in two dimensions. It is a two-dimensional conformal field theory whose symmetry algebra is the Virasoro algebra with the central charge c = 1 2 . Correlation functions of the spin and energy operators are described by the ( 4 , 3 ) minimal model. While the minimal model has been exactly solved, see also, e.g., the article on Ising critical exponents, the solution does not cover other observables such as connectivities of clusters.