The similarity of a given manifold to one of these objects can be measured with the Willmore energy. A vanishing at rank 4 higher than their dimension is among few established patterns in these objects’ chaotic higher homotopy groups. A 3-dimensional one of these objects is expressed as a fiber bundle over a 2-dimensional one in the Hopf fibration. John Milnor constructed an “exotic” class of these objects, whose eversion was described by Stephen Smale. Any simply-connected closed 3-manifold is homeomorphic to one of these objects by (*) Perelman’s proof of the Poincaré conjecture. A coordinate system named for these objects uses azimuthal and polar angles and has a Jacobian from Cartesian coordinates of rho squared times sine of phi. For 10 points, name these shapes consisting of all points a fixed distance away from their center. ■END■
ANSWER: n-sphere [accept S-n; accept with any positive integer in place of “n”; accept circles]
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