of each product equals its marginal cost, the theorem can be derived. The price of cloth should be: (1) with P(C) standing for the price of cloth, r standing for rent paid to landowners, w for wage levels and a and b respectively standing for the amount of land and labor used, and do not change with the prices of goods. Similarly, the price of wheat would be: (2) with P(W) standing for the price of wheat, r and w for rent and wages, and c and d for the respective amount of land and labor used, and also considered to be constant. If, then, cloth experiences a rise in its price, at least one of its factors must also become more expensive, for equation 1 to hold true, since the relative amounts of labor and land are not affected by changing prices. It can be assumed that it would be labor—the factor that is intensively used in the production of cloth—that would rise. When wages rise, rent must fall, in order for equation 2 to hold true. But a fall in rent also affects equation 1. For it to still hold true, then, the rise in wages must be more than proportional to the rise in cloth prices. A rise in the price of a product, then, will more than proportionally raise the return to the most intensively used factor, and decrease the return to the less intensively used factor. Criticism The validity of the Heckscher–Ohlin model has been questioned since the classical Leontief paradox. Indeed, Feenstra called the Heckscher–Ohlin model "hopelessly inadequate as an explanation for historical and modern trade patterns". As for the Stolper–Samuelson theorem itself, Davis and Mishra recently stated, "It is time to declare Stolper–Samuelson dead". They argue that the Stolper–Samuelson theorem is "dead" because following trade liberalization in some developing countries (particularly in Latin America), wage inequality rose, and, under the assumption that these countries are labor-abundant, the SS theorem predicts that wage inequality should have fallen. Aside from the declining trend in wage inequality in Latin America that has followed trade liberalization in the longer run (see Lopez-Calva and Lustig), an alternative view would be to recognize that technically the SS theorem predicts a relationship between output prices and relative wages. Papers that compare output prices with changes in relative wages find moderate-to-strong support for the Stolper–Samuelson theorem for Chile, Mexico, and Brazil.