The independence number of uncrowded hypergraphs: bounds matching the shattering threshold
Pith reviewed 2026-06-26 23:49 UTC · model grok-4.3
The pith
Uncrowded k-uniform hypergraphs contain independent sets reaching the shattering threshold up to a (1-ε) factor.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
For every ε>0 and k≥2, every n-vertex k-uniform uncrowded hypergraph of sufficiently large maximum degree Δ contains an independent set of size at least (1-ε)n ((1/(k-1))(log Δ/Δ))^{1/(k-1)}. This attains the shattering-threshold constant, resolves a folklore conjecture by providing the first pseudorandom class matching the threshold, and resolves the Verstraëte-Wilson conjecture by showing linear hypergraphs have independence number at least c_k n (log Δ/Δ)^{1/(k-1)} with c_k=1-o_k(1). The proofs are constructive and give Õ(nΔ)-time randomized static algorithms and Õ(1)-round randomized LOCAL algorithms.
What carries the argument
The uncrowded condition, a quantitative restriction on edge intersections, which allows the independence number bound to reach the shattering threshold via a constructive probabilistic argument.
If this is right
- Uncrowded hypergraphs form the first pseudorandom class whose independence number matches the shattering threshold.
- Linear hypergraphs satisfy the independence number lower bound with leading constant 1-o_k(1).
- There is an Õ(nΔ)-time randomized algorithm to find an independent set of the stated size in uncrowded hypergraphs.
- There is an Õ(1)-round randomized LOCAL algorithm to find such an independent set.
Where Pith is reading between the lines
- The constructive algorithms may adapt to produce large independent sets in other restricted hypergraph families that are close to uncrowded.
- The matching of the shattering threshold supplies a deterministic combinatorial analog to the geometry observed in random constraint satisfaction instances.
- The result suggests checking whether the (1-ε) factor can be removed entirely for sufficiently structured subclasses of uncrowded hypergraphs.
Load-bearing premise
The input hypergraph must be uncrowded and have sufficiently large maximum degree Δ.
What would settle it
An explicit construction of a k-uniform uncrowded hypergraph with large Δ whose largest independent set is smaller than (1-ε)n ((1/(k-1))(log Δ/Δ))^{1/(k-1)} for some fixed ε>0.
Figures
read the original abstract
A foundational theorem of Ajtai, Koml\'os, Pintz, Spencer, and Szemer\'edi asserts that every $n$-vertex $k$-uniform uncrowded hypergraph with maximum degree $\Delta$ contains an independent set of size $c_k n{\left(\frac{\log \Delta}{\Delta}\right)^{\frac{1}{k-1}}}$, for some constant $c_k>0$. Determining the optimal leading constant $c_k$ in this bound is a major open problem. A natural target is the so-called shattering-threshold constant $\left(\frac{1}{k-1}\right)^{\frac{1}{k-1}}$, which appears in the solution-space geometry of random constraint satisfaction problems, in average-case complexity theory, and in statistical physics, among other areas. We prove that uncrowded hypergraphs attain this threshold. More precisely, for every $\epsilon>0$ and $k\geq 2$, every $n$-vertex $k$-uniform uncrowded hypergraph of sufficiently large maximum degree $\Delta$ contains an independent set of size at least $(1-\epsilon) n {\left(\frac{1}{k-1}\frac{\log \Delta}{\Delta}\right)^{\frac{1}{k-1}}}$. Consequently, we obtain the first pseudorandom class of hypergraphs whose guaranteed independence number matches the shattering threshold, resolving a folklore conjecture. Moreover, as another direct consequence, we resolve a conjecture of Verstra\"ete and Wilson by proving that there exists a constant $c_k=1-o_k(1)$ such that every $n$-vertex $k$-uniform linear hypergraph of maximum degree $\Delta$ has independence number at least $c_k n\left(\frac{\log \Delta}{\Delta}\right)^{\frac{1}{k-1}}$. Our techniques are constructive yielding efficient algorithms for both static and distributed settings. Specifically, we provide an $\tilde O(n\Delta)$-time randomized static algorithm and an $\tilde O(1)$-round randomized $\textsf{LOCAL}$ algorithm to find an independent set in uncrowded hypergraphs at the shattering threshold. These results extend seamlessly to the the setting of linear hypergraphs.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The manuscript proves that for every ε>0 and k≥2, every n-vertex k-uniform uncrowded hypergraph with sufficiently large maximum degree Δ contains an independent set of size at least (1-ε)n ((1/(k-1))(log Δ/Δ))^{1/(k-1)}. This matches the shattering-threshold constant up to a (1-ε) factor. The result extends immediately to linear hypergraphs (with leading constant 1-o_k(1)) and yields an Õ(nΔ)-time randomized static algorithm together with an Õ(1)-round randomized LOCAL algorithm.
Significance. If the central probabilistic argument holds, the work resolves the folklore conjecture on the optimal leading constant for uncrowded (hence linear) hypergraphs, supplies the first pseudorandom class attaining the shattering threshold, and upgrades the classical Ajtai–Komlós–Pintz–Spencer–Szemerédi theorem with a parameter-free leading constant once Δ is large. The constructive nature of the proofs (refined deletion/LLL tailored to the uncrowded codegree condition) is a notable strength.
minor comments (3)
- [§2] §2: the uncrowded condition is invoked from the AKPS-S literature; a one-sentence self-contained definition would aid readers who do not consult the reference.
- [Algorithms section] The Õ notation in the algorithmic statements hides polylog(Δ) factors; an explicit statement of the dependence on k and ε would improve precision.
- [Introduction] The extension from uncrowded to linear hypergraphs is stated as immediate, but a one-line justification of the inclusion linear ⊂ uncrowded would eliminate any ambiguity.
Simulated Author's Rebuttal
We thank the referee for their positive and accurate summary of the manuscript, for recognizing its resolution of the folklore conjecture on the shattering threshold for uncrowded hypergraphs, and for recommending acceptance.
Circularity Check
No significant circularity detected
full rationale
The central claim upgrades the leading constant in the AKPS-S theorem for uncrowded hypergraphs from some positive c_k to (1-ε) times the shattering threshold via a self-contained probabilistic argument (refined deletion/LLL exploiting the uncrowded intersection condition to control codegrees). The uncrowded hypothesis and large-Δ assumption are used directly to absorb lower-order terms without any fitted parameter, self-citation chain, or definitional reduction; the extension to linear hypergraphs is immediate by inclusion. No load-bearing step reduces to a prior result by the same authors or renames an input as output.
Axiom & Free-Parameter Ledger
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