I was at that talk by David which is the first link. Highly recommended watch, he is such a good presenter. The way he went full circle there and had the room in raucous applause at the end was something I never forgot.

Thanks for the links! If Haskell is more your style than Racket, there's a Haskell version of the implementation tutorial at https://davidchristiansen.dk/tutorials/implementing-types-hs... .

The Strange Loop talk was very enjoyable. You are a gifted public speaker. And I just want to say that I am excited to read your book on Lean in full, too!