### Over 4500 Entries in the nLab, and Its 2nd Birthday!

#### Posted by David Corfield

*guest post by Zoran Škoda*

The first entry of the *n*-Category Lab wiki appeared on November 28, 2008 02:18:19 marking the creation of the *n*Lab; hence this Sunday morning it is 2 years old! Three days before the birthday its nominal count of pages reached 4500. This may be a proper moment to celebrate its wide usability already at its tender age and even more to invite people to use it more, and if possible to contribute. Like in our earlier update from May, we would like to point to some highlights in $n$Lab. But I somewhat run out of steam to dwell this time on the content and will rather outline some improvements in the *content organization* of the $n$Lab which may make it more attractive to you.

In my impression, in its first year, the $n$Lab was focused on our daily research needs and central areas of our interest: category theory, including higher, topoi, homotopy theory, topology, sheaves, stacks, simplicial objects, descent, cohomology (including differential), foundations and categorical aspects of physics. I have received signals from some users of $n$Lab that they do not contribute because they “do more concrete things”, say Lie algebras, representation theory, mathematical physics and so on and feel they do not wish to write about categories. But this is a misunderstanding: more stuff in related areas is *very* welcome and we *need* contributors telling us the story in nearby areas of algebra, mathematical physics, differential geometry and so on (of course, not that far an area that we can not understand, appreciate and connect to).

Seeing that we started in rather self-centered areas of *categorical mathematics*, it was difficult, in the first year, for a newcomer, to navigate through *n*Lab and find out what interesting things (s)he can find there. Hence, in the last several months a great amount of activity was centered not only in creating new content but also around new lists/tables of pointers of content in particular fields of interest. In this vein, Urs has been very enthusiastic in adding floating tables of contents. For example, each entry in topos theory, e.g. subobject classifier has a floating table of contents for Topos theory on its right-hand side. It is a pull-down menu which helps you navigate through entries in the subject of the particular table. Even the HomePage uses one floating table, to help the newcomer, and there are top level tables for mathematics and for physics. One can navigate top-down to some subsubjects from there.

Another organizational change in the last year or so is that most discussions which would earlier take place in query boxes in $n$Lab entries shifted to the nForum, which is well structured for many-purpose activities, thanks to the software and maintenance care of Andrew Stacey. Some of the discussions are about spams, bugs, writing, future policies and software, while some are about mathematical research, where Todd, Toby, Urs, Domenico, Jim, Tim, Mike, John, David and others explain extensively to each other their insights. Some of the longer among such discussions happen in the Atrium section, especially under Mathematics, Physics and Philosophy.

I have personally made the effort to connect $n$Lab to the external sources of information and replaced the previous Online Resources page by a network of several resource pages including:

- top page math resources
- page math blogs (previous Online Resources) with list of blogs and wikis
- page math institutions with a selected list of top world institutes and links to AMS-maintained and some other lists of math societies and departments
- page math archives with a list of main archives of online content in areas of our interest; with few exceptions (like MathSciNet), subscription sites are avoided and free archives preferred
- page math resources by individuals where there are some extremely rich pages of individuals in the
*prime*areas of $n$Lab (there are hundreds of pages on individual mathematicians in $n$Lab, here we list just few particularly useful links) - page books and reviews in mathematical physics with selected list of major research level books in mathematical physics

While in the first year the physics entries were dwarfed by the mathematical part of $n$Lab, now we do have a non-negligeable physics content. We recommend an outline of the nPOV in physics in the entry (mainly by Urs Schreiber)

Some picture of $n$Lab’s physics content can be accessed from the links at the top page physicscontents.

## Re: Over 4500 entries in the nLab and its 2nd birthday!

This is great! Happy birthday, $n$Lab. Having 4,500 articles already is really stunning. It also happens to be

mybirthday today, too — I wish I’d gained as much knowledge in the past 2 years as the $n$Lab has :).