industries into an oligarchy of survivors. Mature industries do not attract new capital because of low returns. Mature companies with large amounts of capital invested and brand recognition can also try to block new competitors in their markets. See also secular stagnation theory. The use of credit instruments to reduce capital costs for new production. The scholarly controversy about the TRPF among Marxists and non-Marxists has continued for a hundred years. There exist nowadays several thousands of academic publications on the TRPF worldwide. However, no book is available which provides an exposition of all the different arguments that have been made. Professor Michael C. Howard stated that "The connection between profit and economic theory is an intimate one. (...) However, a generally accepted theory of profit has not emerged at any stage in the history of economics... theoretical controversies remain intense." Dispute over existence Okishio's theorem The Japanese economist Nobuo Okishio notably argued in 1961, "if the newly introduced technique satisfies the cost criterion [i.e. if it reduces unit costs, given current prices] and the rate of real wage remains constant", then the rate of profit must increase. Assuming constant real wages, technical change would lower the production cost per unit, thereby raising the innovator's rate of profit. The price of output would fall, and this would cause the other capitalists' costs to fall also. The new (equilibrium) rate of profit would therefore have to rise. By implication, the rate of profit could in that case only fall if real wages rose in response to higher productivity, squeezing profits. This theory is sometimes called neo-Ricardian, because David Ricardo also claimed that a fall in the average rate of profit could ordinarily be brought about only by rising wages (one other scenario could be, that foreign competition would drive down the local market prices for outputs, causing falling profits). Criticism John E. Roemer criticized the absence of fixed capital in Okishio's model, and therefore modified Okishio's model, to include the effect of fixed capital. He concluded though that:It is also possible to construct an alternative Okishio-type model, in which the rising cost of land rents (or property rents) lowers the industrial rate of profit. Competition David Ricardo, interpreting Adam Smith's falling rate of profit theory to be that increased competition drives down the average rate of profit, argued that competition could only level out differences in profit rates on investments in