Categorial progress …

I paperbacked my gentle introductory notes on category theory sooner than ideally I would have wished. But with routine-but-major heart surgery scheduled unexpectedly early, I thought I should at least get a beta version of the book out while I could, not knowing what the future would hold.

In the last week or so, I’ve started returning to the book, since a number of issues with it have been nagging away at me. Indeed, I now have a list of well over a hundred notes-to-self, ranging from “Must be more consistent in the use of ‘one-one’ vs ‘one-to-one’’’, through relatively easy-to-fix queries like “Even if I don’t prove that the arrow is monic in a topos, can’t I at least arm-wavingly say why it morally ought to be?”, and then on to heavier issues like “Maybe I really should say something about Tarski–Grothendieck universes?”, “Since I do explain about products of arrows , shouldn’t I at least say something about how this leads on to the idea of monoidal categories?”. And so on.

Working through these queries is therefore going to keep me merrily busy for some weeks as I put together a Version 1.2 of the notes. So far, delving back into elementary category theory has indeed been pretty enjoyable, not least because (and here I tempt fate) I haven’t yet found any really embarrassing mistakes in Version 1.1. Long may that last! But if you have spotted foul-ups, large or small, or have more general suggestions for improving a section, now is the time to let me know!

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