Erdős's high-girth Steiner system conjecture

Given nq>r2n\ge q>r\ge2, an (n,q,r)(n,q,r)-Steiner system is a collection of qq-element subsets of an nn-element set in which every rr-element subset lies in exactly one block. A (j,i)(j,i)-configuration is a set of ii blocks spanning at most jj vertices. Erdős's conjecture. For every integer g2g\ge2, there exists ngn_g such that for all admissible nngn\ge n_g, there exists an (n,3,2)(n,3,2)-Steiner system with no (i+2,i)(i+2,i)-configuration for all 2ig2\le i\le g. This was fully proved by Kwan, Sah, Sawhney, and Simkin, while earlier work established approximate versions.

Sources & referencesView supporting material

Primary source

Michelle Delcourt and Luke Postle, “Finding an almost perfect matching in a hypergraph avoiding forbidden submatchings”, arXiv:2204.08981 (2024).

Additional references

2 papers in this index state this conjecture (2018–2022). The statement above is taken from the most recent of them; the others are arXiv:1802.04227.

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