Today, the London Algebra Colloquium began a new year, and a new phase in its history. The Colloquium met at City University for the first time. No institution which was not a college or (in Imperial’s case recently) an ex-college of the University of London has ever been part of the consortium.

I will have to make new headers for the colloquium records!

The history-making talk was a remarkable performance by Robert Marsh, describing his joint work with Jeanne Scott. He first gave us a complete definition of a cluster algebra (no mean feat in itself), then explained carefully how there is a cluster algebra structure on the coordinate ring of a Grassmannian; then we had Postnikov diagrams, illustrated in real time by an example; and finally, the matching polynomial of a weighted bipartite graph sitting in the Postnikov diagram turned out to be a renormalised version of the function expressing a “twisted” Plücker coordinate in terms of the cluster variables. Phew!

If you want to know more, you should have been at the talk …

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## About Peter Cameron

I count all the things that need to be counted.