New results of Bollob\'{a}s-type theorem for affine subspaces and projective subspaces

TL;DR

This paper extends Bollobás-type theorems to affine and projective subspaces over finite fields, providing new bounds and confirming conjectures, with implications for combinatorics and graph theory.

Contribution

It establishes a new upper bound for affine subspace families without restrictions on q, constructs sharp examples, and verifies Hegedüs's conjecture for q=2.

Findings

New upper bound for affine subspaces valid for all q

Construction of affine subspace pairs achieving the bound

Verification of Hegedüs's conjecture when q=2

Abstract

Bollob\'{a}s-type theorem has received a lot of attention due to its application in graph theory. In 2015, G\'{a}bor Heged{\"u}s gave an upper bound of bollob\'{a}s-type affine subspace families for $q\neq 2$, and constructed an almost sharp affine subspaces pair families. In this note, we prove a new upper bound for bollob\'{a}s-type affine subspaces without the requirement of $q\neq 2$, and construct a pair of families of affine subspaces, which shows that our upper bound is sharp. We also give an upper bound for bollob\'{a}s-type projective subspaces, and prove that the Heged{\"u}s's conjecture holds when $q=2$.