text: Paul Samuelson showed how this thing could resolve Pareto inefficiencies in an overlapping generationsmodel where interest rates are below the population growth rate.
full_question: Paul Samuelson showed how this thing could resolve Pareto inefficiencies in an overlapping generationsmodel where interest rates are below the population growth rate. Karl Polanyi called this thing, along withland and labor, one of the three "commodity fictions" in The Great Transformation. The set of interest rateoutputcombinations where the demand for this equals its supply traces out the LM curve in the IS-LM model.Stone wheels on the island of Yap are a famous example of an early "fiat" type. Its supply is directlyproportional to the price level according to the "quantity theory" of it, and in most countries the supply iscontrolled by a central bank like the Federal Reserve. For 10 points, name this thing used in exchange. 
first_sentence: Paul Samuelson showed how this thing could resolve Pareto inefficiencies in an overlapping generationsmodel where interest rates are below the population growth rate.
raw_answer: money 