### The Works of Charles Ehresmann

#### Posted by John Baez

Charles Ehresmann’s complete works are now available for free here:

There are 630 pages on algebraic topology and differential geometry, 800 pages on local structures and ordered categories, and their applications to topology, 900 pages on structured categories and quotients and internal categories and fibrations, and 850 pages on sketches and completions and sketches and monoidal closed structures.

That’s 3180 pages!

On top of this, more issues of the journal he founded, *Cahiers de Topologie et Géométrie Différentielle Catégoriques*, will become freely available online.

Andrée Ehresmann announced this magnificent gift to the world on the category theory mailing list, writing:

We are pleased to announce that the issues of the

Cahiers de Topologie et Géométrie Différentielle Catégoriques, from Volume L (2009) to LV (2014) included, are now freely downloadable from the internet site of the Cahiers:http://ehres.pagesperso-orange.fr/Cahiers/Ctgdc.htm

through the hyperlink to Recent Volumes.

In the future the issues of the

Cahierswill become freely available on the site of theCahierstwo years after their paper publication. We recall that papers published up to Volume XLIX are accessible on the NUMDAM site.Moreover, the 7 volumes of

Charles Ehresmann: Oeuvres complètes et commentées(edited by A. Ehresmann from 1980-83 as Supplements to theCahiers) are now also freely downloadable from the sitehttp://ehres.pagesperso-orange.fr/C.E.WORKS

fichiers/C.EWorks.htmThese 2 sites are included in the site of Andrée Ehresmann

http://ehres.pagesperso-orange.fr/

and they can also be accessed through hyperlinks on its first page.

Sincerely,

Andree Ehresmann, Marino Gran and Rene Guitart,

Chief-Editors of the Cahiers

## Re: The Works of Charles Ehresmann

That’s great. Of course, it would be greater still if they were freely available immediately, but I can imagine the kind of reasons why the editors aren’t doing this, and I don’t have a solution.

One reason why I’d really like

Cahiersto be freely available immediately is thatTheory and Applications of Categoriesneeds a competitor.I’m very pro-TAC, I’m an editor, and I want people to submit their best category theory work to it. However, there’s a shortage of attractive journals that publish category theory papers, so the quality within TAC is quite mixed.

Cahiersunfortunately makes itself less attractive by not making its papers freely available immediately (unlike TAC, which does). Of course, authors can arXiv, but it’s not the same.Cahiershas a long and proud history of publishing important papers in category theory, and I’ve been wishing for a while that it could offer the same kind of free-to-everyone service that TAC does.