Stacks

Groups describe symmetries of single objects. The symmetries of families of objects are described by groupoids. If we want to study all families of a certain type of geometric object (Euclidean triangles, say, or Riemann surfaces), we are led to the notion of stack. In this talk I will explain what a stack is and why stacks are useful. I will give a few simple examples. In recent years, algebraic stacks have become an indispensable tool in algebraic geometry, but other areas of geometry should profit from considering stacks, too.

Refreshments will be served at 2:45 p.m. in the Faculty Lounge, Math Annex (Room 1115).