English

Projective and external saturation problem for posets

Combinatorics 2023-06-21 v1

Abstract

We introduce two variants of the poset saturation problem. For a poset PP and the Boolean lattice Bn\mathcal{B}_n, a family F\mathcal{F} of sets, not necessarily from Bn\mathcal{B}_n, is \textit{projective PP-saturated} if (i) it does not contain any strong copies of PP, (ii) for any GBnFG\in \mathcal{B}_n\setminus \mathcal{F}, the family F{G}\mathcal{F}\cup \{G\} contains a strong copy of PP, and (iii) for any two different F,FFF,F'\in\mathcal{F} we have F[n]F[n]F\cap[n]\neq F'\cap [n]. Ordinary strongly PP-saturated families, i.e., subfamilies F\mathcal{F} required to be from Bn\mathcal{B}_n satisfying (i) and (ii), automatically satisfy (iii) as they lie within Bn\mathcal{B}_n. We study what phenomena are valid both for the ordinary saturation number sat(n,P)\mathrm{sat}^*(n,P) and the projective saturation number, the size of the smallest projective PP-saturated family. Note that the projective saturation number might differ for a poset and its dual. We also introduce an even more relaxed and symmetric version of poset saturation, \textit{external saturation}. We conjecture that all finite posets have bounded external saturation number, and prove this in some special cases.

Keywords

Cite

@article{arxiv.2306.10387,
  title  = {Projective and external saturation problem for posets},
  author = {Dömötör Pálvölgyi and Balázs Patkós},
  journal= {arXiv preprint arXiv:2306.10387},
  year   = {2023}
}
R2 v1 2026-06-28T11:07:59.197Z