3 March 2018:
1) I posted another blog article written by students at the ACT2018 school:
* Jonathan Lorand and Fabrizio Genovese, Hypergraph categories of cospans
, The n-Category Café, February 28, 2018.
This is a nice introduction to Brendan's theory of decorated cospans.
2) Kenny Courser and I are close to finishing a paper - close enough that I blogged about it to ask for comments and corrections:
* John Baez, Coarse-graining open Markov processes, The n-Category Café
, March 4, 2018.
You can get the paper from here. If any of you can look through it and find mistakes or things that are hard to understand, please let me know!
3) Christian Williams and I signed contracts to work for Pyrofex, and we had our first conversation with Mike Stay about this project. We'll start by working on ideas in here:
* Mike Stay and Greg Meredith, Representing operational semantics with graph-enriched Lawvere theories
This project should be fun, because it'll connect network theory with computer science... and Mike and Greg actually know a bunch of computer science.
Finally, not really relevant to our grand scheme: I took a little break today by blogging about mathematical logic:
* John Baez, Nonstandard integers as complex numbers
, Azimuth, March 3, 2018.
Briefly: if you start with a nonstandard model of the natural numbers, you can define integers in the usual way (as differences of your nonstandard natural numbers), and then rational numbers (as ratios of integers). So, there are lots of nonstandard versions of the rational numbers! Any one of these gives a field. Now for the cool part: if your nonstandard model of the natural numbers is countable, your field of nonstandard rational numbers can be seen as a subfield of the ordinary complex numbers! This is counterintuitive at first, because we tend to think of nonstandard models of Peano arithmetic as spooky and elusive things, while we tend to think of the complex numbers as well-understood. But I explain why it makes sense.