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# Category Archives: exposition

## Reducts and Reed-Muller codes

While I was in Adelaide, supposedly on holiday, Csaba Szabó sent me a preprint of a paper he had written with his student Bertalan Bodor. I read it with interest, and was able to make a small remark on the … Continue reading

## Perth, week 1

The first week of the visit is over. The weather has been quite cold, but it is likely to improve as time goes on. The best day so far was yesterday, when we went to Yanchep National Park and had … Continue reading

Posted in doing mathematics, exposition
Tagged derangements, H. Zantema, Jordan's theorem
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## Arrays

This post is about things called triple arrays, and some variants. I was visited by Tomas Nilson last semester, and we have just posted a paper on the arXiv. This is a subject with a quite extraordinary history; Rosemary will … Continue reading

Posted in exposition
Tagged Agrawal, double array, sesqui-array, square 2-design, symmetric BIBD, Tomas Nilson, triple array
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## Pappus and Diophantus

This post is inspired by a nice article by Adrian Rice and Ezra Brown in the latest BSHM Bulletin, titled “Commutativity and collinearity: a historical case study of the interconnection of mathematical ideas, Part II”. Pappus’ Theorem states that, if … Continue reading

Posted in exposition, history
Tagged Fano plane, Kirkman, Pappus' Theorem, Steiner triple system, two squares equality
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## Conventions

I woke this morning thinking about something I learned in physics at school. A wire carrying a current in a magnetic field is acted on by a force (if it is not parallel to the field): in what direction does … Continue reading

## There is no McLaughlin geometry

Congratulations to Patric Östergård and Leonard Soicher, who have just completed a big computation whose conclusion is “There is no McLaughlin geometry”. The run-time of the computation was about 250 core-years. So what did they compute, and why does it … Continue reading