The Octoberfest is a noble tradition in category theory: a low-key, friendly conference for researchers to share their work and thoughts. This year it’s on Saturday October 26th and Sunday October ...

I called this chapter of my course “Relations”, but I should have called it “Specifying subsets and functions”, because that’s what it’s all about. This week, we saw that it’s possible to define ...

Oct 10, 2024 John Baez, Joe Moeller and Todd Trimble have a new paper out that rethinks the splitting principle in the context of categorified rigs, or ‘2-rigs’.

Oct 18, 2024 In Week 5 of my ETCS-based set theory course, I explained how to specify subsets and functions by formulas.

Arkani-Hamed has the amusing, informal yet clear manner of someone like Feynman or Coleman. And he explains, step by step, how imaginary particle physicists in some other universe could have invented ...

This phase of the course is all about building up the basic apparatus. We’ve stated our axioms, and it might seem like they’re not very powerful. It’s our job now to show that, in fact, they’re ...

John Baez, Joe Moeller and Todd Trimble, 2-rig extensions and the splitting principle. Our paper categorifies a famous method for studying vector bundles, called the ‘splitting principle’. But it also ...

7. For every function f: X → Y f: X \to Y and element y ∈ Y y \in Y, we can form the fibre f − 1 (y) f^{-1}(y). Category theorists will recognize this as a special case of the existence of pullbacks.