Ever since I first encountered it at school, I've always admired the elegant simplicity of the reductio ad absurdum proof of the irrationality of the square-root of two. I know, I know: I really should get out more.

This week's *New Scientist* includes a description of Euclid's equally elegant and simple, 2,300-year-old, *reductio ad absurdum* proof that there is an infinite number of prime numbers. I hadn't seen it before. It's really neat. The description goes as follows:

Suppose a mathematician comes with a finite list of primes and claims there are no more. Euclid showed that there must be a prime missing from the list. Multiply all the primes on the list together and then add one to this number. This new number is not divisible by any of the primes on the list because you always get remainder one. So Euclid's new number is either another prime itself or divisible by a prime that is missing from the list. If you add this new prime to the list, repeating Euclid's trick will always show that any finite list is missing a prime.

Sorry to bore you with maths. The real reason I'm doing it is because I just thought of the *here's looking at Euclid* pun, and I really didn't want to let it to go to waste.

Just who do you think you are,

Jean-Pierre Petit?Never heard of her!

http://www.amazon.co.uk/Heres-Looking-at-Euclid-Not-Looking-at-Euclid-Petit-Jean-Pierre-Aventures-Danselme-Lanturlu-/dp/0865760926/ref=sr_11_1/026-7444471-1193207?ie=UTF8

The clues are there. And now for our home and studio audience, but not the panel .......

Hey! She's stolen my joke, then travelled backwards in time and written a book about it! Damn devious, those Belgians!

More to her than meets the eye - i fear that she might be a he.

http://www.jp-petit.com/bio_en/bio_en.htm

Probablyon his fourth glass too, judging by the photograph

Never trust a man named Jean.

particularly not one who's worked out how to charge £86.02 for his (or her) book - see Amazon for details!