ENTRY, EXIT, AND DIFFUSION WITH LEARNING BY DOING
早期进入者单位产出收入更高，晚期进入者通过向先入者学习降低生产成本。连续时间完美预见均衡下，竞争产生S形扩散和交错进出，垄断者创新更少但更早。
Early entry has the advantage of higher revenues per unit of output early on. Late entry has the benefit of learning from the experience of earlier entrants, and hence lower production costs. The advantages are balanced off in a continuous-time, perfect-foresight equilibrium. Competition generates S-shaped diffusion, and staggered entry and exit. A monopolist will innovate less than a competitive industry, but the innovation that he does do, he will do sooner. Copyright 1989 by American Economic Association.