Problem 1: What do Eaton and Kortum see as Ricardo's main insight?
Problem 2: What problems do with the original version of the theory do they think made it difficult to apply in practice?
Problem 3: How do they think recent innovations have helped make the theory relevant again?
(Paper Source: Eaton, J., & Kortum, S. (2012). Putting Ricardo to Work. Journal of Economic Perspectives, 26(2), 65-90.)