The so-called purchasing-power parity (PPP) puzzle takes one of two forms. In its first form, early tests of the PPP-hypothesis failed to reject unit roots in real exchange rates, thus rejecting the hypothesis of PPP holding in the long term. In the more recent literature, the literature on the...

For set-indexed partial sums processes of stationary mixing random fields, convergence of finite dimensional distributions to a Brownian motion is proved, extending to infinite variance previous results of the author and a Central Limit Theorem of Nahapetian. Gibbs fields are considered.