The entire contents of the 3rd edition of *Category theory for computing science, *by Michael Barr and Charles Wells*, *is now available online at either of these addresses:

http://www.abstractmath.org/CTCS/ctcs.pdf

ftp.math.mcgill.ca/barr/pdffiles/ctcs.pdf

We have submitted it to be published by Theory and Application of Categories in their reprint series. That is where Triples, Toposes and Theories is published.

There are two distinct versions of parts of CTCS already available on the internet. Neither of them contain all the material in the book, nor do they contain answers to all the exercises, as the copy available above does.

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