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arXiv 0912.20022009-12-10math.MGmath.CV

Rigidity of configurations of balls and points in the $N$-sphere

Edward Crane, Ian Short

备注：: 12 pages, 3 figures

英文摘要：

We answer two questions of Beardon and Minda that arose from their study of the conformal symmetries of circular regions in the complex plane. We show that a configuration of closed balls in the $N$-sphere is determined up to Möbius transformations by the signed inversive distances between pairs of its elements, except when the boundaries of the balls have a point in common, and that a configuration of points in the $N$-sphere is determined by the absolute cross-ratios of 4-tuples of its elements. The proofs use the hyperboloid model of hyperbolic $(N+1)$-space.

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