Basic Category Theory by Tom Leinster.
From the webpage:
Basic Category Theory is an introductory category theory textbook. Features:
- It doesn’t assume much, either in terms of background or mathematical maturity.
- It sticks to the basics.
- It’s short.
Advanced topics are omitted, leaving more space for careful explanations of the core concepts. I used earlier versions of the text to teach master’s-level courses at the University of Glasgow.
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The book is published by Cambridge University Press. You can find all the publication data, and buy it, at the book’s CUP web page.
It was published on 24 July 2014 in hardback and e-book formats. The physical book should be in stock throughout Europe now, and worldwide by mid-September. Wherever you are, you can (pre)order it now from CUP or the usual online stores.
By arrangement with CUP, a free online version will be released in January 2016. This will be not only freely downloadable but also freely editable, under a Creative Commons licence. So, for instance, if parts of the book are unsuitable for the course you’re teaching, or if you don’t like the notation, you can change it. More details will appear here when the time comes.
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Freely available as etext (6 months after hard copy release) and freely editable?
Show of hands. How many publishers have you seen with those policies?
I keep coming up with one, Cambridge University Press, CUP.
As readers and authors we need to vote with our feet. Purchase from and publish with Cambridge University Press.
It may take a while but other publishers may finally notice.