An uniform version of Dvir and Moran's theorem

TL;DR

This paper extends Dvir and Moran's theorem to uniform families of sets, providing an upper bound on their size based on VC-dimension, using a uniform version of the Croot-Lev-Pach polynomial method.

Contribution

It introduces a uniform version of Dvir and Moran's theorem and proves it using a uniform polynomial method, broadening the applicability of VC-dimension bounds.

Findings

Establishes an upper bound of 2 times the binomial coefficient for uniform families.

Provides a uniform polynomial lemma analogous to Croot-Lev-Pach.

Extends non-uniform bounds to uniform set families with VC-dimension constraints.

Abstract

Dvir and Moran proved the following upper bound for the size of a family $\mbox{$\cal F$}$ of subsets of $[n]$ with $\mbox{Vdim}(\mbox{$\cal F$} \Delta \mbox{$\cal F$})\leq d$. Let $d\leq n$ be integers. Let $\mbox{$\cal F$}$ be a family of subsets of $[n]$ with $\mbox{Vdim}(\mbox{$\cal F$} \Delta \mbox{$\cal F$})\leq d$. Then \[ \left|\mbox{$\cal F$}\right|\le 2\sum_{k=0}^{\lfloor d/2 \rfloor}\binom nk. \] Our main result is the following uniform version of Dvir and Moran's result. Let $d\leq n$ be integers. Let $\mbox{$\cal F$}$ be an uniform family of subsets of $[n]$ with $\mbox{Vdim}(\mbox{$\cal F$} \Delta \mbox{$\cal F$})\leq d$. Then \[ \left|\mbox{$\cal F$}\right|\le 2 {n \choose \lfloor d/2 \rfloor}. \] Denote by $\mathbf{v_F}\in \{0,1\}^n$ the characteristic vector of a set $F \subseteq [n]$. Our proof is based on the following uniform version of Croot-Lev-Pach Lemma: Let $0\leq d\leq n$ be integers. Let $\mbox{$\cal H$}$ be a $k$-uniform family of subsets of $[n]$. Let $\mathbb F$ be a field. Suppose that there exists a polynomial $P(x_1, \ldots ,x_n,y_1, \ldots ,y_n)\in \mathbb F[x_1, \ldots ,x_n,y_1, \ldots ,y_n]$ with $\mbox{deg}(P)\leq d$ such that $P(\mathbf{v_F},\mathbf{v_F})\ne 0$ for each $F\in \mbox{$\cal H$}$ and $P(\mathbf{v_F},\mathbf{v_G})= 0$ for each $F\ne G\in \mbox{$\cal H$}$. Then \[ \left|\mbox{$\cal H$}\right|\le 2 {n \choose \lfloor d/2 \rfloor}. \]