English

Extremal structure in dense arrangements of $k$-intersecting curves

Combinatorics 2026-05-21 v1

Abstract

Let PP be a set of nn points in the plane, and let C\mathcal C be a collection of nn simple kk-intersecting curves, meaning that every two distinct curves of C\mathcal C meet in at most kk points. A classical theorem of Pach and Sharir from 1998 gives the upper bound I(P,C)=Ok(n(3k+1)/(2k+1))I(P,\mathcal C)=O_k(n^{(3k+1)/(2k+1)}). We prove that this bound can be improved when one excludes a complete local incidence pattern. More precisely, for any fixed integers s>k+12s>k+1\ge 2, if there do not exist ss points of PP such that every (k+1)(k+1)-tuple among them is contained in a distinct curve of C\mathcal C, then I(P,C)=o(n(3k+1)/(2k+1))I(P,\mathcal C)=o(n^{(3k+1)/(2k+1)}). In the special case of pseudo-segments, this extends Solymosi's theorem on dense point-line arrangements to dense arrangements of pseudo-segments.

Keywords

Cite

@article{arxiv.2605.20705,
  title  = {Extremal structure in dense arrangements of $k$-intersecting curves},
  author = {Andrew Suk and Su Zhou},
  journal= {arXiv preprint arXiv:2605.20705},
  year   = {2026}
}