English

Largest component in Boolean sublattices

Combinatorics 2025-03-18 v2 Discrete Mathematics

Abstract

For a subfamily F2[n]{F}\subseteq 2^{[n]} of the Boolean lattice, consider the graph GFG_{F} on F{F} based on the pairwise inclusion relations among its members. Given a positive integer tt, how large can F{F} be before GFG_{F} must contain some component of order greater than tt? For t=1t=1, this question was answered exactly almost a century ago by Sperner: the size of a middle layer of the Boolean lattice. For t=2nt=2^n, this question is trivial. We are interested in what happens between these two extremes. For t=2gt=2^{g} with g=g(n)g=g(n) being any integer function that satisfies g(n)=o(n/logn)g(n)=o(n/\log n) as nn\to\infty, we give an asymptotically sharp answer to the above question: not much larger than the size of a middle layer. This constitutes a nontrivial generalisation of Sperner's theorem. We do so by a reduction to a Tur\'an-type problem for rainbow cycles in properly edge-coloured graphs. Among other results, we also give a sharp answer to the question, how large can F{F} be before GFG_{F} must be connected?

Cite

@article{arxiv.2411.07985,
  title  = {Largest component in Boolean sublattices},
  author = {Julian Galliano and Ross J. Kang},
  journal= {arXiv preprint arXiv:2411.07985},
  year   = {2025}
}

Comments

23 pages, 2 figures; v2 includes minor corrections from review; to appear in Acta Mathematica Hungarica

R2 v1 2026-06-28T19:57:24.066Z