Test of Guttmann and Enting's conjecture in the eight-vertex model

We investigate the analyticity property of the partially resummed series expansion (PRSE) of the partition function for the eight-vertex model. By developing a graphical technique, we have obtained the first few terms of the PRSE and found that these terms have a pole only at one point in the complex plane of the coupling constant. This result supports the conjecture proposed by Guttmann and Enting concerning the "solvability" in statistical mechanical lattice models.