English

Extensions of the Colorful Helly Theorem for $d$-collapsible and $d$-Leray complexes

Combinatorics 2023-05-23 v1

Abstract

We present extensions of the Colorful Helly Theorem for dd-collapsible and dd-Leray complexes, providing a common generalization to the matroidal versions of the theorem due to Kalai and Meshulam, the ``very colorful" Helly theorem introduced by Arocha, B\'ar\'any, Bracho, Fabila and Montejano, and the ``semi-intersecting" colorful Helly theorem proved by Montejano and Karasev. As an application, we obtain the following extension of Tverberg's Theorem: Let AA be a finite set of points in Rd\mathbb{R}^d with A>(r1)(d+1)|A|>(r-1)(d+1). Then, there exist a partition A1,,ArA_1,\ldots,A_r of AA and a subset BAB\subset A of size (r1)(d+1)(r-1)(d+1), such that i=1rconv((B{p})Ai)\cap_{i=1}^r \text{conv}( (B\cup\{p\})\cap A_i)\neq\emptyset for all pABp\in A\setminus B. That is, we obtain a partition of AA into rr parts that remains a Tverberg partition even after removing all but one arbitrary point from ABA\setminus B.

Keywords

Cite

@article{arxiv.2305.12360,
  title  = {Extensions of the Colorful Helly Theorem for $d$-collapsible and $d$-Leray complexes},
  author = {Minki Kim and Alan Lew},
  journal= {arXiv preprint arXiv:2305.12360},
  year   = {2023}
}

Comments

20 pages, 1 figure