English

Monochromatic Sumsets in Countable Colourings of Abelian Groups

Combinatorics 2024-07-08 v1

Abstract

Fern\'andez-Bret\'on, Sarmiento and Vera showed that whenever a direct sum of sufficiently many copies of Z4{\mathbb Z}_4, the cyclic group of order 4, is countably coloured there are arbitrarily large finite sets XX whose sumsets X+XX+X are monochromatic. They asked if the elements of order 4 are necessary, in the following strong sense: if GG is an abelian group having no elements of order 4, is it always the case there there is a countable colouring of GG for which there is not even a monochromatic sumset X+XX+X with XX of size 2? Our aim in this short note is to show that this is indeed the case.

Keywords

Cite

@article{arxiv.2407.03938,
  title  = {Monochromatic Sumsets in Countable Colourings of Abelian Groups},
  author = {Imre Leader and Kada Williams},
  journal= {arXiv preprint arXiv:2407.03938},
  year   = {2024}
}