Also, there are strong and (somewhat) profound links between double crochet and low-dimensional differential geometry: when you're crocheting, you're basically creating a 2-manifold by choosing its Gaussian curvature at every stitch.
The amusing thing is that since the resulting crocheted object is flexible, you're not really choosing the way that the surface sits in space when you're crocheting: you're really only generating the intrinsic geometry of the surface. The distinction between intrinsic and embedded geometry is probably one of the biggest ideas you see in a grad school differential geometry class, and was one of the big advances in differential geometry a century ago or so. (I'm a combinatorist, not a differential geometer, so I'd be happy to be corrected on any of the above points - but I believe that I'm correct)
Wikipedia's already collected most of the links that I would have posted here: http://en.wikipedia.org/wiki/Mathematics_and_fiber_arts