In the strategy discussion, I wrote:

> All told, I propose an Azimuth quest with the following focus:
> - Pursuit of applications of Petri nets to stochastic as well as deterministic epidemiology

This is wide open.

Here is one idea I had, which I posted to the Azimuth blog:

> Modeling each country separately leaves holes in the overall model for a pandemic. E.g. if the curve goes down, travel restrictions are lifted, and then it goes back up due to what’s happening in other countries. Compartmental models use ODEs and assume a well-mixed population. What about a multi-level approach, where each country or well-mixed region has a compartmental model with its own parameters. Then there could be transitions between the compartments in different countries, reflecting flows due to travel. This looks like a potential application of composition of open networks. Perhaps a good composition rule could produce an aggregated, abstracted compartmental model for the whole globe. Or help us in other ways to understand the dynamics of the whole.

Posted to:

* [How scientists can help fight Covid-19](, John Baez, Azimuth blog, March 31.

Spelled out, the suggestion is to apply the open Petri net framework that John, Jade and Blake have been developing to the composition of global pandemic networks from smaller regional networks.

* [Open Petri nets](, John C. Baez, Jade Master, Aug 2018.

* [A compositional framework for reaction networks](, John C. Baez, Blake S. Pollard, April 2017.