Holroyd–Talbot–Borg conjecture for intersecting faces of simplicial complexes

Let Δ\Delta be a simplicial complex whose smallest facet has dd vertices. For a vertex vv of Δ\Delta, let linkΔv\operatorname{link}_{\Delta}v denote its link, and let fr1(linkΔv)f_{r-1}(\operatorname{link}_{\Delta}v) be the number of faces of dimension r1r-1 in that link. Let A\mathcal{A} be a family of pairwise-intersecting faces of Δ\Delta, each with rr elements.

Holroyd–Talbot–Borg conjecture. If rd/2r\leq d/2, then there is some vertex vv of Δ\Delta such that

Afr1(linkΔv).|\mathcal{A}|\leq f_{r-1}(\operatorname{link}_{\Delta}v).

If equality holds and r<d/2r<d/2, then A\mathcal{A} consists of the rr-element faces containing some vertex vv.

This extends Erdős–Ko–Rado-type results from uniform set systems and independence complexes of graphs to arbitrary simplicial complexes. The source presents it as the question raised by Holroyd and Talbot and extended by Borg; its resolution is not specified here.

Sources & referencesView supporting material

Primary source

Denys Bulavka and Russ Woodroofe, “Strict Erdős-Ko-Rado theorems for simplicial complexes”, arXiv:2503.15608 (2025).

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