I want to go back over something from Part 11, but in a more systematic way that I hope is easier to follow. I’m stating these facts roughly now, to not get bogged down. But I’ll state them precisely, ...

Dec 15, 2024 More detail on the Cycle Length Lemma, a basic result in the theory of random permutations. We prove a categorified version of this result, which is an equivalence of groupoids, and then ...

As a digression from our usual fare on the n n -Café, here’s one of my favorites, about an early theory of the Solar System, ...

Nov 22, 2024 The final chapter of this course on secretly-categorical set theory. Axiomatic Set Theory 9: The Axiom of Choice Nov 15, 2024 The penultimate week of this axiomatic set theory course, ...

Earlier this month the Mathematics Institute at Uppsala University hosted a conference called Categorification in Algebra and Topology, clearly a theme close to our collective heart. As yet there are ...

The Eighth International Conference on Applied Category Theory ( https://easychair.org/cfp/ACT2025) will take place at the University of Florida on June 2-6, 2025. The conference will be preceded by ...

This is the homepage for the UT Geometry and Quantum Field Theory Seminar. At the organizational meeting we will flesh out the details of our plans for the semester. Below are some suggestions to get ...

Nov 1, 2022 John Baez is giving a talk on categories and epidemiology on Wednesday November 2nd, viewale online at noon UTC. A Categorical Understanding of the Proof of Cantor-Schröder-Bernstein? Dec ...

for all infinite sets X X and Y Y. Proving this required most of the concepts and results from the second half of the course: well ordered sets, the Cantor–Bernstein theorem, the Hartogs theorem, Zorn ...