English

A counterexample to a geometric Hales-Jewett type conjecture

Combinatorics 2014-10-13 v2

Abstract

P\'or and Wood conjectured that for all k,l2k,l \ge 2 there exists n2n \ge 2 with the following property: whenever nn points, no l+1l + 1 of which are collinear, are chosen in the plane and each of them is assigned one of kk colours, then there must be a line (that is, a maximal set of collinear points) all of whose points have the same colour. The conjecture is easily seen to be true for l=2l = 2 (by the pigeonhole principle) and in the case k=2k = 2 it is an immediate corollary of the Motzkin-Rabin theorem. In this note we show that the conjecture is false for k,l3k, l \ge 3.

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Cite

@article{arxiv.1409.0362,
  title  = {A counterexample to a geometric Hales-Jewett type conjecture},
  author = {Vytautas Gruslys},
  journal= {arXiv preprint arXiv:1409.0362},
  year   = {2014}
}

Comments

4 pages, 2 figures; updated title, added figures and more details