I was at the Heriot-Watt semigroup day on Friday (at which I was one of a surprising number of category theorists).

It was only after I'd got there that I realised I should have been wearing my No2ID T-shirt...

Q: What's yellow and equivalent to the Axiom of Choice?
A: Zorn's Lemon.

You've probably all heard that one before. But here's one I invented, which is even better¹

Q: Which member of the university hierarchy is equivalent to the Axiom of Choice and frequently eats at Norwegian restaurants?
A: The whale-ordering Principal.

Thank you very much, ladies and gentlemen; I'm here all week.

¹ ie, worse.