How to Count n-Ary Trees How do you count rooted planar n-ary trees with a given number of leaves? Use Lagrange inversion! TeXnical Issues Sage advice on viewing this blog and posting comments thereon ...

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How do you count rooted planar n -ary trees with some number of leaves? For n = 2 this puzzle leads to the Catalan numbers. These are so fascinating that the combinatorist Richard Stanley wrote a ...

In week241 of This Week’s Finds, you can follow me on my tour of the Laser Interferometry Gravitational-Wave Observatory in Louisiana: Also hear some tales of the dodecahedron… from the pyritohedron ...

This week in our seminar on Cohomology and Computation we continued discussing the bar construction, and drew some pictures of a classic example ...

Christoph Wockel asks me to forward the following question to the n n-Café: What is a reference for a generalisation of the following canonical cocycle to higher dimensions? Thanks for any hints. My ...

The math-blogosphere is abuzz with interest in the new Math Overflow, a mathematics questions and answers site. Already we at the Café have been helped with the answer to a query on the Fourier ...

John Baez has been struggling to understand the pi calculus — a formalism for modelling concurrency in computer science. I’m going to try to explain it nice and slowly. I’ll use the “polyadic ...

This fall I’m also teaching a seminar on quantization and cohomology. Derek Wise is taking notes, which you can get as PDF files here: John Baez and Derek Wise, Quantization and Cohomology. I’ll ...

Merry Christmas! It’s still Christmas here in California, despite what the time stamp on this blog may say. So, it’s not too late for one last present! Here’s one just for you, from Santa and his ...

A while back Gina asked why computer scientists should be interested in categories. Maybe you categorical computer scientists out there have your own favorite answers to this? I’d be glad to hear them ...

Category Theory and Biology Posted by David Corfield Some of us at the Centre for Reasoning here in Kent are thinking about joining forces with a bioinformatics group. Over the years I’ve caught ...