|Presenter||Richard Garner (Macquarie University)|
|Author(s)||Dr Richard Garner|
|Session||Category Theory, Algebraic Topology, K-Theory|
Ultrafilters are important structures in areas of mathematics as diverse as combinatorics, model theory, topology and dynamical systems. In this talk, I explain how the notions of ultrafilter, ultrapower, product of ultrafilters, and Rudin--Keisler ordering of ultrafilters, are all encapsulated in the following result: the category of finite-coproduct-preserving endofunctors of the category of sets is a presheaf category.