Sunflowers in set systems of bounded dimension

TL;DR

This paper advances the understanding of sunflower existence in set families with bounded VC-dimension, providing near-conditional bounds and verifying related conjectures for Littlestone dimension and geometric set systems.

Contribution

It extends sunflower conjecture results to families with bounded VC-dimension and verifies Erdős-Rado conjecture for Littlestone dimension and certain geometric set systems.

Findings

Sunflowers exist in VC-bounded families under specific size conditions.

Erdős-Rado conjecture holds for families with bounded Littlestone dimension.

Verification of the conjecture for some geometrically defined set systems.

Abstract

Given a family $\mathcal F$ of $k$-element sets, $S_1,\ldots,S_r\in\mathcal F$ form an {\em $r$-sunflower} if $S_i \cap S_j =S_{i'} \cap S_{j'}$ for all $i \neq j$ and $i' \neq j'$. According to a famous conjecture of Erd\H os and Rado (1960), there is a constant $c=c(r)$ such that if $|\mathcal F|\ge c^k$, then $\mathcal F$ contains an $r$-sunflower. We come close to proving this conjecture for families of bounded {\em Vapnik-Chervonenkis dimension}, VC-dim$(\mathcal F)\le d$. In this case, we show that $r$-sunflowers exist under the slightly stronger assumption $|\mathcal F|\ge2^{10k(dr)^{2\log^{*} k}}$. Here, $\log^*$ denotes the iterated logarithm function. We also verify the Erd\H os-Rado conjecture for families $\mathcal F$ of bounded {\em Littlestone dimension} and for some geometrically defined set systems.