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Trudy Matematicheskogo Instituta imeni V.A. Steklova, 2015, Volume 288, Pages 224–229
DOI: https://doi.org/10.1134/S037196851501015X
(Mi tm3597)
 

$(n,m)$-fold covers of spheres

Imre Bárányab, Ruy Fabila-Monroyc, Birgit Vogtenhuberd

a Department of Mathematics, University College London, UK
b Alfréd Rényi Institute of Mathematics, Hungary Academy of Sciences, Budapest, Hungary
c Departamento de Matemáticas, Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional (CINVESTAV), México, D.F. CP 07360, México
d Institute for Software Technology, Graz University of Technology, Graz, Austria
References:
Abstract: A well-known consequence of the Borsuk–Ulam theorem is that if the $d$-dimensional sphere $S^d$ is covered with less than $d+2$ open sets, then there is a set containing a pair of antipodal points. In this paper we provide lower and upper bounds on the minimum number of open sets, not containing a pair of antipodal points, needed to cover the $d$-dimensional sphere $n$ times, with the additional property that the northern hemisphere is covered $m>n$ times. We prove that if the open northern hemisphere is to be covered $m$ times, then at least $\lceil(d-1)/2\rceil+n+m$ and at most $d+n+m$ sets are needed. For the case of $n=1$ and $d\ge2$, this number is equal to $d+2$ if $m\le\lfloor d/2\rfloor+1$ and equal to $\lfloor(d-1)/2\rfloor+2+m$ if $m>\lfloor d/2\rfloor+1$. If the closed northern hemisphere is to be covered $m$ times, then $d+2m-1$ sets are needed; this number is also sufficient. We also present results on a related problem of independent interest. We prove that if $S^d$ is covered $n$ times with open sets not containing a pair of antipodal points, then there exists a point that is covered at least $\lceil d/2\rceil+n$ times. Furthermore, we show that there are covers in which no point is covered more than $n+d$ times.
Funding agency Grant number
European Research Council 267165
Hungarian Academy of Sciences K 83767
CONACYT - Consejo Nacional de Ciencia y Tecnología 153984
The first author was partially supported by the ERC Advanced Research Grant no. 267165 (DISCONV) and by the Hungarian National Research Grant K 83767. The second author was partially supported by grant 153984 (CONACyT, Mexico).
Received in September 2014
English version:
Proceedings of the Steklov Institute of Mathematics, 2015, Volume 288, Pages 203–208
DOI: https://doi.org/10.1134/S0081543815010150
Bibliographic databases:
Document Type: Article
UDC: 515.1
Language: English
Citation: Imre Bárány, Ruy Fabila-Monroy, Birgit Vogtenhuber, “$(n,m)$-fold covers of spheres”, Geometry, topology, and applications, Collected papers. Dedicated to Professor Nikolai Petrovich Dolbilin on the occasion of his 70th birthday, Trudy Mat. Inst. Steklova, 288, MAIK Nauka/Interperiodica, Moscow, 2015, 224–229; Proc. Steklov Inst. Math., 288 (2015), 203–208
Citation in format AMSBIB
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\by Imre~B\'ar\'any, Ruy~Fabila-Monroy, Birgit~Vogtenhuber
\paper $(n,m)$-fold covers of spheres
\inbook Geometry, topology, and applications
\bookinfo Collected papers. Dedicated to Professor Nikolai Petrovich Dolbilin on the occasion of his 70th birthday
\serial Trudy Mat. Inst. Steklova
\yr 2015
\vol 288
\pages 224--229
\publ MAIK Nauka/Interperiodica
\publaddr Moscow
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\crossref{https://doi.org/10.1134/S037196851501015X}
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    Труды Математического института имени В. А. Стеклова Proceedings of the Steklov Institute of Mathematics
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