Copyright © 2004 Elsevier B.V. All rights reserved.
Geometric permutations of disjoint unit spheres
Received 16 December 2003;
revised 9 August 2004;
accepted 21 August 2004.
Communicated by Mark de Berg.
Available online 13 November 2004.
References and further reading may be available for this article. To view references and further reading you must purchase this article.
Abstract
We show that a set of n disjoint unit spheres in admits at most two distinct geometric permutations if n
9, and at most three if 3
n
8. This result improves a Helly-type theorem on line transversals for disjoint unit spheres in : if any subset of size at most 18 of a family of such spheres admits a line transversal, then there is a line transversal for the entire family.
Keywords: Geometric permutation; Line transversal; Unit sphere; Unit ball; Hadwiger-type theorem; Helly-type theorem







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