with x 0 = 1 . This particular case of the Z N model is often called the FZ model in its own right, after V.A. Fateev and A.B. Zamolodchikov who first calculated this solution. The FZ model approaches the XY model in the limit as N → → ∞ ∞ . It is also a special case of the chiral Potts model and the Kashiwara–Miwa model.