Journal ArticleWe examine ordered, periodic, Ising models on a sq lattice at varying levels x of frustration. The thermodynamic singularity of the fully frustrated model (x=1) is at T=0 while those of partially frustrated lattices (0<x<1) occur at finite Tc . The critical indices in the partially frustrated lattices that we consider-including the logarithmic specific heat-are all identical to those in the ferromagnet (x=0.) We display exact values of Tc and of ground-state energy and entropy Eo and So , at x=1, 2/3, 1/2 , 2/5 ,...,0
