Talagrand's bounded-uniformity fractional expectation threshold conjecture

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Let XX be a finite set, let k∈Nk\in\mathbb{N} satisfy k≤log⁡L∣X∣k\leq\log_L|X|, and let g ⁣:\mleft(Xk\mright)→[0,1]g\colon{\mleft(\kern-.1em\genfrac{}{}{0pt}{}{X}{k}\kern-.1em\mright)}\to[0,1]. Define <g>\left<g\right> by

\left<g\right>:=\left\{S\in 2^X\mathrel{\left|}\sum_{T\subseteq S}g(T)\geq 1\right.\right\},

and for a family G⊆2XG\subseteq 2^X define w(G,p):=∑S∈Gp∣S∣w(G,p):=\sum_{S\in G}p^{|S|}, with w(g,p)w(g,p) defined analogously. The bounded-uniformity conjecture. There exists a fixed L>1L>1 such that, for all finite sets XX, all such kk, all such functions gg, and all p∈[0,1]p\in[0,1], if w(g,p)=1w(g,p)=1, then there exists a set G⊆2X∖{∅}G\subseteq2^X\setminus\{\emptyset\} such that <g>⊆<G>\left<g\right>\subseteq\left<G\right> and

w(G,pL)≤1.w\left(G,\frac{p}{L}\right)\leq1.

This is a restricted form of Talagrand's conjecture whose resolution would imply the full conjecture. Results cited in the source cover constant-size support, and current quantitative bounds do not establish this claim in general.

References

Primary source

Thomas Fischer and Yury Person, “Further remarks on fractional vs. expectation thresholds”, arXiv:2505.21782 (2025).

Additional references

3 papers in this index state this conjecture (2021–2025). The statement above is taken from the most recent of them; the others are arXiv:2311.08163, arXiv:2105.10905.

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