I was looking in the mathematics department of our local academic bookshop (Blackwell's) yesterday and came across a book on crocheting hyperbolic surfaces. I can't trace the book right now, but this site gives an idea of what they look like:
This is not a great deal of use for anything except demonstrating geometry. It also has the teensy-weensy problemette that you can't buy hyperbolic fabric to back it, so each patch has to have its own backing (Suffolk puffs would work). And the example in the book is rather crude and ugly - the crochet work is much more attractive.
I'm kinda tempted to try it.
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