English

A 910-block explicit construction guaranteeing a triple intersection with every $6$-subset of $[60]$

Combinatorics 2026-02-05 v1

Abstract

We present a simple explicit family B\mathcal{B} of 910910 66-subsets of [60]={1,,60}[60]=\{1,\dots,60\} such that every 66-subset S[60]S\subset[60] intersects at least one block BBB\in\mathcal{B} in at least three elements, i.e.\ SB3|S\cap B|\ge 3. Equivalently, B\mathcal{B} is a covering (dominating set) of the Johnson graph J(60,6)J(60,6) with covering radius 33 in the Johnson metric. The construction is purely combinatorial, based on a fixed split of [60][60] into two halves, a pairing of each half, and a pigeonhole argument. We also record a crude counting lower bound and a straightforward generalization to [2m][2m] (with mm even).

Cite

@article{arxiv.2602.04867,
  title  = {A 910-block explicit construction guaranteeing a triple intersection with every $6$-subset of $[60]$},
  author = {Paulo Henrique Cunha Gomes},
  journal= {arXiv preprint arXiv:2602.04867},
  year   = {2026}
}
R2 v1 2026-07-01T09:36:30.157Z