English

A system of disjoint representatives of line segments with given $k$ directions

Combinatorics 2021-01-11 v1

Abstract

We prove that for all positive integers nn and kk, there exists an integer N=N(n,k)N = N(n,k) satisfying the following. If UU is a set of kk direction vectors in the plane and JU\mathcal{J}_U is the set of all line segments in direction uu for some uUu\in U, then for every NN families F1,,FN\mathcal{F}_1, \ldots, \mathcal{F}_N, each consisting of nn mutually disjoint segments in JU\mathcal{J}_U, there is a set {A1,,An}\{A_1, \ldots, A_n\} of nn disjoint segments in 1iNFi\bigcup_{1\leq i\leq N}\mathcal{F}_i and distinct integers p1,,pn{1,,N}p_1, \ldots, p_n\in \{1, \ldots, N\} satisfying that AjFpjA_j\in \mathcal{F}_{p_j} for all j{1,,n}j\in \{1, \ldots, n\}. We generalize this property for underlying lines on fixed kk directions to kk families of simple curves with certain conditions.

Keywords

Cite

@article{arxiv.2101.02887,
  title  = {A system of disjoint representatives of line segments with given $k$ directions},
  author = {Jinha Kim and Minki Kim and O-Joung Kwon},
  journal= {arXiv preprint arXiv:2101.02887},
  year   = {2021}
}