Sequential innovation, patents, and imitation
认为，当创新是序贯且互补的时，专利保护对鼓励创新的作用不如静态情形，竞争和模仿反而可能提高发明者的预期利润，并用软件行业的自然实验证据支持这一观点。
We argue that when innovation is “sequential” (so that each successive invention builds in an essential way on its predecessors) and “complementary” (so that each potential innovator takes a different research line), patent protection is not as useful for encouraging innovation as in a static setting. Indeed, society and even inventors themselves may be better off without such protection. Furthermore, an inventor's prospective profit may actually be enhanced by competition and imitation. Our sequential model of innovation appears to explain evidence from a natural experiment in the software industry.