Consider the metric space on, say, &#8477;<sup>2</sup> induced by the various $L^p$ norms, and the group of isometries from that space into itself that preserve the origin. When $p=2$ I get the continuous group of rotations, but when $p\in\{1,3,4,5,...\infty\}$ it looks like I just get $D_8$, the symmetry group of the square. Question: what's going on here? Why is 2 so special? Are there other natural norms on &#8477;<sup>2</sup> (or on &#8477;<sup>n</sup>) besides the euclidean one that give interesting isometry groups?