i will discuss in detail some work of joe kohn involving subelliptic estimates. i hope to provide an understandable account of some of the technical matters from his 1979 acta paper, and i will discuss some of my own work on points of finite type.  although there is no new theorem to present, i will provide several new approaches to these ideas. to prevent the talk from being too technical, i will also include several elementary interludes that can be understood by graduate 2022年亚洲世界杯预选赛 .