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Comment by Ceezy | Hacker News Reader

If anybody interested the best book to learn the category theory: https://www.maths.ed.ac.uk/~v1ranick/papers/maclanecat.pdf

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Mac Lane was one of the founders of category theory - see for example:

"General Theory of Natural Equivalences" - Samuel Eilenberg and Saunders MacLane. Transactions of the American Mathematical Society, Vol. 58, No. 2, (Sep., 1945), pp. 231-294

His "Categorical algebra" paper from 1964 is open-access:

https://projecteuclid.org/euclid.bams/1183526392

When his book came out it was the standard work for a while. I think some of the terminology he uses is no longer standard, and there are now many very good modern introductions. But his book is still a pretty good read, primarily because he was a wonderful writer with a very distinctive style.

That said, the examples (given the time the book was written) are almost exclusively mathematical. The proofs and exercises are usually not difficult, but at a high level of abstraction (not surprisingly).

This book is intended for a "working mathematician." Also, the subject has progressed since the book was written.

For anyone else interested, Tom Leinster (also of Edinburgh Uni) has also written a good short book for beginners:

https://www.maths.ed.ac.uk/~tl/bct/

I did his course at uni that used this book as a basis and it was great. Tough, but great.

Why do you think this is the best book? And would someone's background, or lack thereof, in other fields of mathematics not have a bearing on that assessment?

If someone lacks interest in math I’m not sure category theory makes sense even in the FOMO way.

To someone who is not interested in math per se but rather in its applications to engineering, category theory, too, has something to offer.

Cause that's it's reputation in math circles. And recommended by most of my teachers. Also because I used it a lot. You don't need to read it top to bottom. I think people here are interested by monoid and stuff. But to do the monoid part you don't really need category. An Algebra course about monoid is good enough actually.

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