English

An Erd\H{o}s--Szekeres type result for words with repeats

Combinatorics 2026-05-27 v4

Abstract

We prove an Erd\H{o}s--Szekeres type result for finite words over N\mathbb{N} with repeated values. Specifically, we define a \emph{repeat} in a word to be an occurrence of a value which is not its first occurrence. We define an occurrence of a \emph{pattern} π\pi in a word ww to be a (not necessarily consecutive) subword of ww that is order isomorphic to π\pi. In this note, we show that every word with kn6+1kn^6+1 repeats contains one of the following patterns: 0k+20^{k+2}, 0011nn0011\cdots nn, nn1100nn\cdots1100, 012n012n012 \cdots n012 \cdots n, 012nn210012 \cdots nn\cdots 210, n210012nn\cdots 210012\cdots n, n210n210n\cdots 210n\cdots 210. Moreover, when k=1k=1, we show that this is best possible by constructing a word with n6n^6 repeats that does not contain any of these patterns.

Keywords

Cite

@article{arxiv.2510.23573,
  title  = {An Erd\H{o}s--Szekeres type result for words with repeats},
  author = {Kyle Celano and Abigail Ollson and Niraj Velankar and Jun Yan},
  journal= {arXiv preprint arXiv:2510.23573},
  year   = {2026}
}

Comments

11 pages, 9 figures