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  1. Home > Articles & Issues >
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  3. An Erdős--Szekeres t ...
Article

An Erdős--Szekeres type result for words with repeats

Kyle Celano (1), Abigail Ollson (2), Niraj Velankar (3), Jun Yan (4)
(1) Wake Forest University
(2) Keele University
(3) Universität Greifswald
(4) University of Oxford
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Open on arXiv
Submitted on
October 28, 2025
Accepted on
May 14, 2026
Published on
May 20, 2026
Last modified on
May 20, 2026
Special issue 28
vol. 28:1, Permutation Patterns 2025
Special issues
DOI
10.46298/dmtcs.16801
License
Attribution 4.0 International (CC BY 4.0)
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263
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159
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An Erdős--Szekeres type result for words with repeats

Kyle Celano (1), Abigail Ollson (2), Niraj Velankar (3), Jun Yan (4)
(1) Wake Forest University
(2) Keele University
(3) Universität Greifswald
(4) University of Oxford
Abstract
We prove an Erdős--Szekeres type result for finite words over $\mathbb{N}$ 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} $π$ in a word $w$ to be a (not necessarily consecutive) subword of $w$ that is order isomorphic to $π$. In this note, we show that every word with $kn^6+1$ repeats contains one of the following patterns: $0^{k+2}$, $0011\cdots nn$, $nn\cdots1100$, $012 \cdots n012 \cdots n$, $012 \cdots nn\cdots 210$, $n\cdots 210012\cdots n$, $n\cdots 210n\cdots 210$. Moreover, when $k=1$, we show that this is best possible by constructing a word with $n^6$ repeats that does not contain any of these patterns. 11 pages, 9 figures
Keywords
  • Combinatorics
Mathematics Subject Classification 2020
  • 05A05 - Permutations, words, matrices
  • 05A15 - Exact enumeration problems, generating functions
  • 68Q45 - Formal languages and automata
  • 68R10 - Graph theory (including graph drawing) in computer science
  • 68R15 - Combinatorics on words
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