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SUMMARY:Péter Ágoston
DTSTART:20201009T120000Z
DTEND:20201009T133000Z
DTSTAMP:20260423T021128Z
UID:BBCG/4
DESCRIPTION:Title: <a href="https://researchseminars.org/talk/BBCG/4/">A l
 ower bound on the number of colours needed to nicely colour a sphere</a>\n
 by Péter Ágoston as part of Budapest Big Seminar on Combinatorics + Geom
 etry\n\n\nAbstract\nThe Hadwiger--Nelson problem is about determining the 
 chromatic number of the plane (CNP)\, defined as the minimum number of col
 ours needed to colour the plane so that no two points of distance 1 have t
 he same colour. I will talk about the related problem for spheres\, with a
  few natural restrictions on the colouring. Thomassen showed that with the
 se restrictions\, the chromatic number of all manifolds satisfying certain
  properties (including the plane and all spheres with a large enough radiu
 s) is at least 7. We prove that with these restrictions\, the chromatic nu
 mber of any sphere with a large enough radius is at least 8. This also giv
 es a new lower bound for the minimum colours needed for colouring the 3-di
 mensional space with the same restrictions.\n
LOCATION:https://researchseminars.org/talk/BBCG/4/
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