The conjectured fractional codegree threshold for generalized Steiner systems

For integers nr2n\geq r\geq 2, a fractional (r1,r,n)(r-1,r,n)-Steiner system in an rr-uniform hypergraph HH is a function φ:E(H)R0\varphi:E(H)\to\mathbb{R}_{\geq0} such that degHφ(p)=1\deg_H^\varphi(p)=1 for every (r1)(r-1)-set pV(H)(r1)p\in V(H)^{(r-1)}. Fractional Steiner-system threshold conjecture. The minimum codegree threshold for a fractional (r1,r,n)(r-1,r,n)-Steiner system is

(r1)nr+Θ(1).\frac{(r-1)n}{r}+\Theta(1).

This generalizes the paper's parity-based lower-bound construction and asks for the asymptotically sharp fractional codegree threshold; it remains open.

Sources & referencesView supporting material

Primary source

Michael Zheng, “Codegree conditions for (fractional) Steiner triple systems”, arXiv:2411.07981 (2026).

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