The spin-spin correlation functions in the ground state of certain 2D
fully frustrated Ising models fall off with distance with exponent eta
= 1/2. This is known both numerically and from calculations that are
special to each model. This value of the exponent contrasts with eta =
1/4 for the unfrustrated systems at T-c. The purpose of this paper is
to develop a common method that is applicable to both frustrated and
unfrustrated systems.