English

Rainbow Tur\'an problems for forbidden subposets

Combinatorics 2025-11-21 v2

Abstract

A family G\mathcal{G} of sets is a copy of a poset (P,)(P,\leqslant) if (G,)(\mathcal{G},\subseteq) is isomorphic to (P,)(P,\leqslant). The forbidden subposet problem asks for determining La(n,P)La^*(n,P), the maximum size of a family F2[n]\mathcal{F}\subseteq 2^{[n]} that does not contain any copy of PP. We study the rainbow version of this problem: what is the maximum size LaR(n,P)La_R^*(n,P) of a family F=i=1mAi\mathcal{F}=\cup_{i=1}^mA^i such that all AiA^i are antichains and there is no copy of PP with all sets coming from distinct AiA^i or equivalently F\mathcal{F} admits a proper coloring (sets FFF\subset F' must receive different colors) with no rainbow copy of PP. A poset (Q,)(Q,\leqslant') rainbow forces (P,)(P,\leqslant) if any proper coloring cc of QQ (qqq\leqslant' q' or qqq'\leqslant' q implies c(q)c(q)c(q)\neq c(q')) admits a rainbow copy of PP. We establish connection between the LaLa^* and the LaRLa^*_R functions via poset rainbow forcing, determine the asymptotics of LaR(n,T)La_R^*(n,T) for all tree posets and obtain further exact or asymptotic results for antichains and complete bipartite posets.

Keywords

Cite

@article{arxiv.2511.14298,
  title  = {Rainbow Tur\'an problems for forbidden subposets},
  author = {Balázs Patkós},
  journal= {arXiv preprint arXiv:2511.14298},
  year   = {2025}
}
R2 v1 2026-07-01T07:42:53.874Z