# You're reading: cp’s mathem-o-blog

### Porl Air-dursh: a public service announcement

Since we’re all talking and writing about Paul Erdős today, I just thought I’d make a little post clearing up how to write, and how to say, his name.

### Talk: Computability of Bass-Serre structures in the Grzegorczyk hierarchy

I’m going to abuse this here organ of mine to show off a thing I did yesterday.

My chum the inimitable David Cushing has started a postgrad pure maths seminar at Newcastle. Because there are only a few pure postgrads here, he asked me to give a talk about the stuff I was looking at for the PhD I gave up on last year.

The title of the talk was “Computability of Bass-Serre structures in the Grzegorczyk hierarchy”. It gave an outline of everything needed to show that the fundamental group of a graph of groups is computable in a level of the Grzegorczyk hierarchy at most one higher than its constituent parts, and what that means.

The slides, a recording of the talk, and a link to my presentation template are in a post on my mathem-o-blog: Talk: Computability of Bass-Serre structures in the Grzegorczyk hierarchy

### Relatively Prime is done

This is the first Monday in quite a while that I haven’t had a new episode of Relatively Prime to listen to. That’s because all eight episodes have now been released. I meant to put a little post up each week reminding you to listen to the latest episode, but I completely forgot to do that, so here’s a post saying you can now listen to the whole lot. And you should.

### Newcastle MathsJam October 2012 Recap

I’ve posted my recollections of what happened at last month’s Newcastle MathsJam over at my mathem-o-blog.

### Cardboard SKI calculus

I had a spare day yesterday so, rather than clean my house, I made a model of the SKI combinator calculus out of a pizza box.

[youtube url=http://www.youtube.com/watch?v=fZQMmgElRMI]

### Using Computer Modern on the web

Computer Modern is the family of typefaces developed by Donald Knuth for TeX. It’s so good-looking that some scientists do research just so they can write it up in Computer Modern.

I love TeX and everybody knows it, so I was pretty delighted to hear that the cm-unicode project compiles versions of the Computer Modern fonts in a few formats, including TTF. Having the fonts in TTF format means you can use them in non-TeX environments, in particular on the web.

I’ve run the cm-unicode fonts through codeandmore’s @font-face kit generator to get all the weird formats that the various browsers insist on. The result is a set of packages containing everything you need to use the Computer Modern typefaces on the web.

I’ve put up a page containing examples of each face in use and links to the packages. Enjoy!

### David’s de Bruijn sequence card trick

A few days ago, my friend David asked me if I could help him with a card trick. I said I could, hence this post. I managed to pin David down in front of my camera long enough for him to demonstrate the trick; a full explanation follows this video:

[youtube url=http://www.youtube.com/watch?v=g71wG6RrTL8]