there may not exist any pure strategy Nash equilibrium, the so-called Edgeworth paradox. However, in general there will exist a mixed-strategy Nash equilibrium as shown by Huw Dixon. Moreover, some economists have criticized the model as leading to impractical outcomes in situations, where firms have fixed cost and, as mentioned previously, constant marginal cost, . Hence, the total cost, , of producing units is, . As described in the classic model, prices eventually are driven down to marginal cost, where firms are making zero economic profit and earn no margins on inframarginal units. Thus, firms are not able to recouple any fixed costs. However, if firms have an upward-sloping marginal cost curve, they can earn marginal on infra-marginal sales, which contributes to recouping fixed costs. There is a big incentive to cooperate in the Bertrand model; colluding to charge the monopoly price, , and sharing the market equally, , where is the number of firms in the market. However, not colluding and charging marginal cost is the non-cooperative outcome and the only Nash equilibrium of this model. Therefore, moving from a simultaneous move game to a repeated game with infinite horizon, then collusion is possible because of the Folk Theorem. Bertrand competition versus Cournot competition The Bertrand and Cournot model focus on different aspects of the competitive process, which has led to the model identifying different set of mechanisms that vary the characteristics of the market demand that are exhibited by the firms. Cournot model assumes that the market allocates sales equal to whatever any given firm quantity produced, but at the price level determined by the market. Whereas the Bertrand model assumes that the firm with the lowest price acquires all the sales in the market. When comparing the models, the oligopoly theory suggest that the Bertrand industries are more competitive than Cournot industries. This is because quantities in the Cournot model are considered as strategic substitutes; that is, the increase in quantity level produced by a firm is accommodated by the rival, producing less. Whereas the prices in the Bertrand model are strategic complements; a firm aggressively counters an increase in price level by reducing its price below the rivals. Moreover, both models are criticised based on the assumptions that are made in comparison to the real-world scenario. However, the results from the classic models can be reconciled in a manner of thinking, as presented below. Considering the