Yesterday I wrote a blog article on [categories that show up in probability theory](http://johncarlosbaez.wordpress.com/2013/06/20/relative-entropy-part-1/), as a kind of warmup for finishing off a paper with Tobias Fritz.

This made me want to organize some old notes on this topic. So, I just took some material from the nLab and made it into an Azimuth page:

* [[Experiments in entropy as a functor]].

I have mixed feelings about this material. On the one hand it's rather esoteric and doesn't yet have a "killer app" to justify it. On the other hand, it brings entropy into contact with mathematical ideas that pure mathematicians like, which should someday be useful. And it's cute.