Monochromatic Sumsets in Countable Colourings of Abelian Groups

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Hauptverfasser: Leader, Imre, Williams, Kada
Format: Preprint
Veröffentlicht: 2024
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_version_ 1866910514351702016
author Leader, Imre
Williams, Kada
author_facet Leader, Imre
Williams, Kada
contents Fernández-Bretón, Sarmiento and Vera showed that whenever a direct sum of sufficiently many copies of ${\mathbb Z}_4$, the cyclic group of order 4, is countably coloured there are arbitrarily large finite sets $X$ whose sumsets $X+X$ are monochromatic. They asked if the elements of order 4 are necessary, in the following strong sense: if $G$ is an abelian group having no elements of order 4, is it always the case there there is a countable colouring of $G$ for which there is not even a monochromatic sumset $X+X$ with $X$ of size 2? Our aim in this short note is to show that this is indeed the case.
format Preprint
id arxiv_https___arxiv_org_abs_2407_03938
institution arXiv
publishDate 2024
record_format arxiv
spellingShingle Monochromatic Sumsets in Countable Colourings of Abelian Groups
Leader, Imre
Williams, Kada
Combinatorics
05D10
Fernández-Bretón, Sarmiento and Vera showed that whenever a direct sum of sufficiently many copies of ${\mathbb Z}_4$, the cyclic group of order 4, is countably coloured there are arbitrarily large finite sets $X$ whose sumsets $X+X$ are monochromatic. They asked if the elements of order 4 are necessary, in the following strong sense: if $G$ is an abelian group having no elements of order 4, is it always the case there there is a countable colouring of $G$ for which there is not even a monochromatic sumset $X+X$ with $X$ of size 2? Our aim in this short note is to show that this is indeed the case.
title Monochromatic Sumsets in Countable Colourings of Abelian Groups
topic Combinatorics
05D10
url https://arxiv.org/abs/2407.03938