English

On transversal numbers of intersecting straight line systems and intersecting segment systems

Combinatorics 2021-01-14 v1

Abstract

An intersecting rr-uniform straight line system is an intersecting linear system whose lines consist of rr points on straight line segment of R2\mathbb{R}^2 and any two lines share a point. Recently, the author [A. V\'azquez-\'Avila, \emph{On intersecting straight line systems}, J. Discret. Math. Sci. Cryptogr. Accepted] proved that any intersecting rr-uniform straight line system (P,L)(P,\mathcal{L}) has transversal number at most ν21\nu_2-1, with rν2r\geq\nu_2, where ν2\nu_2 is the maximum cardinality of a subset of lines RLR\subseteq\mathcal{L} such that every triplet of different elements of RR does not have a common point. In this paper, we improve such upper bound if the intersecting rr-uniform straight line system satisfies r=ν2r=\nu_2. This result has immediate consequences for some questions given by Oliveros et al. [D. Oliveros, C. O'Neill and S. Zerbib, \emph{The geometry and combinatorics of discrete line segment hypergraphs}, Discrete Math. {\bf 343} (2020), no. 6, 111825].

Keywords

Cite

@article{arxiv.2101.04708,
  title  = {On transversal numbers of intersecting straight line systems and intersecting segment systems},
  author = {Adrián Vázquez Ávila},
  journal= {arXiv preprint arXiv:2101.04708},
  year   = {2021}
}

Comments

arXiv admin note: text overlap with arXiv:1807.04826 by other authors

R2 v1 2026-06-23T22:05:23.848Z