English

Forbidding $K_{2,t}$ traces in triple systems

Combinatorics 2020-07-08 v2

Abstract

Let HH and FF be hypergraphs. We say HH contains FF as a trace if there exists some set SV(H)S \subseteq V(H) such that HS:={ES:EE(H)}H|_S:=\{E\cap S: E \in E(H)\} contains a subhypergraph isomorphic to FF. In this paper we give an upper bound on the number of edges in a 33-uniform hypergraph that does not contain K2,tK_{2,t} as a trace when tt is large. In particular, we show that limtlimnex(n,Tr3(K2,t))t3/2n3/2=16. \lim_{t\to \infty}\lim_{n\to \infty} \frac{\mathrm{ex}(n, \mathrm{Tr}_3(K_{2,t}))}{t^{3/2}n^{3/2}} = \frac{1}{6}. Moreover, we show 12n3/2+o(n3/2)ex(n,Tr3(C4))56n3/2+o(n3/2)\frac{1}{2} n^{3/2} + o(n^{3/2}) \leq \mathrm{ex}(n, \mathrm{Tr}_3(C_4)) \leq \frac{5}{6} n^{3/2} + o(n^{3/2}).

Keywords

Cite

@article{arxiv.2007.01827,
  title  = {Forbidding $K_{2,t}$ traces in triple systems},
  author = {Ruth Luo and Sam Spiro},
  journal= {arXiv preprint arXiv:2007.01827},
  year   = {2020}
}
R2 v1 2026-06-23T16:50:15.200Z