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Christian Lawson-Perfect

I'm on holiday in the Hague. Here are some of the things I've seen

Spotted this nifty Cairo tiling on my hotel room wall in Den Haag

Intriguing! A brick that's like the 3D analogue of A-series paper: you can cut it in half to produce two bricks similar to the original

never mind , I'm concentrating my efforts on the real future of mathematics:

Mrs L-P had a very happy accident at the photo printers

You know how something can be 'over-engineered'? Well, I think some things are over-mathematicianed.
This bouncy ball, on sale for a couple of quid next to the tills at Mothercare, is a fine example. It's made of six rubber threads, woven together to make a shape with dodecahedral symmetry, such that each face has five different colours. Why six threads? So it can embody the outer automorphism group of \(S_6\)!
It was invented by Dick Esterle. This is my daughter's one; my dog has a bigger one.

I've been told there are colours in this tree.

Recently I discovered a surprising fact about numbers, so I made an online web thing to give it the recognition it deserves. Give it a go:
A little write-up on @aperiodical at

I really love capturing the state of a highly viscous fluid at a snapshot in time, AKA baking a marble cake 🎂 😛

This output is quite aesthetically interesting.

I've been enjoying playing Rikudo Puzzles on android -
It's like Simon Tatham's Signpost game, but on a hexagonal grid. You have to place numbers in the cells to form a contiguous path which fills the entire board. I don't get much out of the timer and stars for finishing quickly - I just like solving the puzzle. Placing numbers can be a bit fiddly - it's very easy to accidentally switch to counting backwards, or miss out a number.

*Alan Partridge voice*
A haar!

(That's a photo of the sea, by the way)

I dreamt that it was possible to draw this in one go without lifting the pen. It involved folding the paper somehow.
It isn't possible, is it?

Never mind screen time, at the moment we're having to limit the baby's lamp time. No idea what's so entrancing about this lamp. 🤔

More mathematical sights on holiday. Beginning to wonder if I'm part of a word problem.

Hands of bananas, helpfully labelled for those who can't count?

I can't not do this, now that I've noticed I've got four bottles, each made up of four parts

I've spent my days working on this toy language for computing with dates. It can finally work out MathsJam dates! It's approximately as efficient as Peano arithmetic 😬