Another not-quite-so-energetic student chiming in. I joined the course late May and just finished the book exercises of chapter 4. At some point my progress in the book got ahead of my progress reading through the lectures (just finishing chapter 2). I think working through the book is a lot more "comfortable" in two senses. First, it lends itself to the "shut up and calculate" mentality and you don't really need to digest the material as much. Second, you don't risk looking dumb in public! But I'm realizing now that the lectures and puzzles contain so many deep, intuitive explanations (both from yourself and the others who've been working through the puzzles "out loud"). So I'm committed to catch up and also interact more on the forums. I agree with the above posters who suggested that the later lectures could be more condensed. In particular, I'm really looking forward to your perspective on toposes. I've been slowly studying Mac Lane + Moerdijk for awhile now, and it's been very encouraging to find it dramatically clearer as I progress in this course. Thank you very much for your effort John. :)