The pic is the phase portrait of a simple "piecewise isometry". Define a map by sliding the two halves of the plane: the top half to the right; the lower half to the left and then rotate. Around each periodic point of the map there's a "periodic island". These are what are in the image...
46 Old books still used dec 29 '12
25 Silly me & Van der Waerden conjecture mar 3 '14
22 Examples of common false beliefs in mathematics jul 3 '11
16 Given a rational number a/b does there exist a finite group G and an automorphism f s.t. f maps exactly a/b elements of G to their own inverses? jan 4 '12
16 Cyclotomic polynomials evaluated at roots of unity sep 1 '12
13 Shannon's communication paper and finite differences jan 20 '11