Four way equivalence model A model that proposes a conceptual link between differences in: interest rates, spot and forward foreign exchange rates, expected inflation rates and the expected change in spot foreign exchange rates. its got a diagram of how its used in BPP text page 333. See also Fisher Effect Purchasing power parity
“the LAW OF ONE PRICE” [PPP] & the “The difference between Spot Rate and forward rate is = Difference between Interest rates of those 2 countries”[IRTP]
which proves the
International Fisher Effect [IFE] and Spot rate = Expected Change in spot rate [Expectations Theory]..