English

Setwise intersecting families of permutations

Combinatorics 2019-12-06 v5 Representation Theory

Abstract

A family of permutations ASnA \subset S_n is said to be \emph{tt-set-intersecting} if for any two permutations σ,πA\sigma, \pi \in A, there exists a tt-set xx whose image is the same under both permutations, i.e. σ(x)=π(x)\sigma(x)=\pi(x). We prove that if nn is sufficiently large depending on tt, the largest tt-set-intersecting families of permutations in SnS_n are cosets of stabilizers of tt-sets. The t=2t=2 case of this was conjectured by J\'anos K\"orner. It can be seen as a variant of the Deza-Frankl conjecture, proved in [4]. Our proof uses similar techniques to those of [4], namely, eigenvalue methods, together with the representation theory of the symmetric group, but the combinatorial part of the proof is harder.

Keywords

Cite

@article{arxiv.1106.0725,
  title  = {Setwise intersecting families of permutations},
  author = {David Ellis},
  journal= {arXiv preprint arXiv:1106.0725},
  year   = {2019}
}

Comments

'Erratum' section added. Yuval Filmus has recently pointed out that Theorem 26 (which was used in the proof of Theorem 25, regarding the case of equality), is false for $t > 1$, so an alternative proof of Theorem 25 has been sketched

R2 v1 2026-06-21T18:17:32.478Z