# Monthly Archives: October 2013

## Cipher 50: Non-trivial evasion

You may have wondered why the last few ciphers have been erratic. The answer is so that the 50th cipher will land exactly on Professor Imre Leader‘s 50th birthday, which was celebrated 14 hours ago. One of the main components … Continue reading

Posted in Activities, Ciphers, Uncategorized | 8 Comments

## Curves of constant width

The 50-pence and 20-pence coins are regular curvilinear heptagons, where each edge is a circular arc centred on the opposite vertex. One may ask why the coins have such an unusual shape. One possible answer is that it is impossible … Continue reading

Posted in Uncategorized | 4 Comments

## Enumerating the rationals

It is a well-known fact, attributed to Cantor, that the set of rationals is countably infinite or, equivalently, we can find a bijection between the rationals and integers. These are easy to construct, but typically quite ugly. If you want … Continue reading

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## Cipher 49: Feline cartograph

This one is entirely graphical: Thanks go to James Aaronson for the design.

## Punting in clearings of arbitrarily small Lebesgue measure

Breaking news: A £500 prize for the most elegant solution in the British Mathematical Olympiad has been founded in the memory of Christopher Bradley, whose contributions to the United Kingdom Mathematics Trust were both plentiful and invaluable. Amongst his portfolio is the bestselling … Continue reading

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## Mathematical innuendo

Here are some primarily mathematical double-entendres conceived by members of the Trinity Mathematicians’ Alcoholic Society. Some of them are biological or particle-physical, but never mind. Also, some names are censored for legal reasons. Disclaimer: I accept no responsibility for any offence caused … Continue reading

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## Mathieu groupoid

You have probably encountered the 15-puzzle, where all but one of the squares of a 4 × 4 grid are occupied by counters. The only acceptable moves are to move a counter into an adjacent unoccupied square. Sam Loyd challenged … Continue reading

Posted in Uncategorized | 3 Comments