Bounding Radon number via Betti numbers

Result code in IS VaVaI

<a href="https://www.isvavai.cz/riv?ss=detail&h=RIV%2F00216208%3A11320%2F20%3A10422349" target="_blank" >RIV/00216208:11320/20:10422349 - isvavai.cz</a>

Result on the web

<a href="https://doi.org/10.4230/LIPIcs.SoCG.2020.61" target="_blank" >https://doi.org/10.4230/LIPIcs.SoCG.2020.61</a>

DOI - Digital Object Identifier

<a href="http://dx.doi.org/10.4230/LIPIcs.SoCG.2020.61" target="_blank" >10.4230/LIPIcs.SoCG.2020.61</a>

Result language

angličtina

Original language name

Bounding Radon number via Betti numbers

Original language description

We prove general topological Radon-type theorems for sets in ℝ^d, smooth real manifolds or finite dimensional simplicial complexes. Combined with a recent result of Holmsen and Lee, it gives fractional Helly theorem, and consequently the existence of weak ε-nets as well as a (p,q)-theorem. More precisely: Let X be either ℝ^d, smooth real d-manifold, or a finite d-dimensional simplicial complex. Then if F is a finite, intersection-closed family of sets in X such that the ith reduced Betti number (with ℤ1 coefficients) of any set in F is at most b for every non-negative integer i less or equal to k, then the Radon number of F is bounded in terms of b and X. Here k is the smallest integer larger or equal to d/2 - 1 if X = ℝ^d; k=d-1 if X is a smooth real d-manifold and not a surface, k=0 if X is a surface and k=d if X is a d-dimensional simplicial complex. Using the recent result of the author and Kalai, we manage to prove the following optimal bound on fractional Helly number for families of open sets in a surface: Let F be a finite family of open sets in a surface S such that the intersection of any subfamily of F is either empty, or path-connected. Then the fractional Helly number of F is at most three. This also settles a conjecture of Holmsen, Kim, and Lee about an existence of a (p,q)-theorem for open subsets of a surface.

Czech name

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Czech description

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Type

D - Article in proceedings

CEP classification

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OECD FORD branch

10101 - Pure mathematics

Project

<a href="/en/project/EF17_050%2F0008466" target="_blank" >EF17_050/0008466: Improvement of internationalization in the field of research and development at Charles University, through the support of quality projects MSCA-IF</a><br>

Continuities

P - Projekt vyzkumu a vyvoje financovany z verejnych zdroju (s odkazem do CEP)

Publication year

2020

Confidentiality

S - Úplné a pravdivé údaje o projektu nepodléhají ochraně podle zvláštních právních předpisů

Article name in the collection

Proceedings of the 36th International Symposium on Computational Geometry (SoCG 2020)

ISBN

978-3-95977-143-6

ISSN

1868-8969

e-ISSN

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Number of pages

13

Pages from-to

1-13

Publisher name

Schloss Dagstuhl--Leibniz-Zentrum für Informatik

Place of publication

Dagstuhl, Germany

Event location

Curych (online)

Event date

Jun 22, 2020

Type of event by nationality

WRD - Celosvětová akce

UT code for WoS article

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