Category Archives: Topology

A common mistake people make is to think that a continuous bijection is a homeomorphism. This is a reasonable mistake. A bijection is an isomorphism of sets.  A bijective homomorphism of groups is an isomorphism of groups. In most algebraic settings I can think of this pattern holds. But it is not true of topologicalContinueContinue reading “Homeomorphism is not just continuous bijection”

I don’t often think about combinatorics, but when I was on a plane recently (coming back from the Netherlands), I started thinking about a question I’ve just kept in the back of my mind for a few years. You can read about the simplex category here. In this blog post I’ll go through the exactContinueContinue reading “Counting the simplex category”