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Extremal $t$-intersecting Families of Permutations for Large $t$

Combinatorics 2026-05-26 v1

Abstract

A set of permutations of {1,2,,n}\{1,2,\dots,n\} is tt-intersecting if any two permutations agree on at least tt inputs. A recent work by Kupavskii, in the spirit of the Erd\H{o}s-Ko-Rado Theorem, shows that for all tnO(nloglognlogn)t\leq n-O\left(\frac{n\log\log n}{\log n}\right), every tt-intersecting family of permutations of {1,2,,n}\{1,2,\dots,n\} with the maximum size must be isomorphic to the set Ak={σ:σ(i)=i for at least t+k indices i{1,2,,t+2k}}A_k = \{\sigma : \sigma(i)=i\text{ for at least } t+k \text{ indices } i\in\{1,2,\dots,t+2k\}\} for some kk. By refining Kupavskii's spread approximation technique, we prove that this conclusion holds for a wider range of tnn5/7+εt\leq n-n^{5/7+\varepsilon}.

Keywords

Cite

@article{arxiv.2605.26051,
  title  = {Extremal $t$-intersecting Families of Permutations for Large $t$},
  author = {Pitchayut Saengrungkongka},
  journal= {arXiv preprint arXiv:2605.26051},
  year   = {2026}
}

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31 pages