Competition among the big and the small
研究大企业和小企业并存的市场，发现大企业进入会通过挤压小企业扩大自身销量，且社会福利随大企业数量增加而上升。
Many industries are made up of a few big firms, which are able to manipulate the market outcome, and of a host of small businesses, each of which has a negligible impact on the market. We provide a general equilibrium framework that encapsulates both market structures. Due to the higher toughness of competition, the entry of big firms leads them to sell more through a market expansion effect generated by the shrinking of the monopolistically competitive fringe. Furthermore, social welfare increases with the number of big firms because the procompetitive effect associated with entry dominates the resulting decrease in product diversity.