A planar algebraic Zarankiewicz theorem over prime fields
Abstract
We prove an incidence bound for bipartite graphs on finite subsets of 𝔽2× 𝔽2 defined by Boolean combinations of polynomial equations of bounded degree. If such a graph is Kk,k-free and its vertex classes have sizes m and n, then it has Ot,k((mn)2/3+m+n+mn/p) edges, where t bounds the description complexity, p is the characteristic of 𝔽, and 1/p=0 in characteristic zero. We also prove this bound for incidences between points and distinct geometrically irreducible components of a two-parameter polynomial family, allowing singular and nonreduced members. The proof extends Lewko's interpolation and contact-multiplicity method from lines to algebraic families. Applications include rich components, polynomial values on difference sets, and polynomial expansion.
Related
BibTeX
@misc{quangham2026planar,
title = {{A planar algebraic Zarankiewicz theorem over prime fields}},
author = {Le Quang-Ham},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.33327},
eprint = {2609.33327},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.33327},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - A planar algebraic Zarankiewicz theorem over prime fields
AU - Le Quang-Ham
PY - 2026
DA - 2026/09/27
PB - arXiv
DO - 10.48550/arxiv.2609.33327
UR - https://arxiv.org/abs/2609.33327
AB - We prove an incidence bound for bipartite graphs on finite subsets of 𝔽^2× 𝔽^2 defined by Boolean combinations of polynomial equations of bounded degree. If such a graph is K_k,k-free and its vertex classes have sizes m and n, then it has O_t,k((mn)^2/3+m+n+mn/p) edges, where t bounds the description complexity, p is the characteristic of 𝔽, and 1/p=0 in characteristic zero. We also prove this bound for incidences between points and distinct geometrically irreducible components of a two-parameter polynomial family, allowing singular and nonreduced members. The proof extends Lewko's interpolation and contact-multiplicity method from lines to algebraic families. Applications include rich components, polynomial values on difference sets, and polynomial expansion.
ER -