Kalai–Meshulam's fractional Helly conjecture for polynomial homological shatter functions

Let dd be a nonnegative integer, let kk be an integer with 0kd0\leq k\leq d, and let A>0A>0. For a set system F\mathcal{F} in Rd\mathbb{R}^d, write δF(d+1)\delta_\mathcal{F}(d+1) for the proportion of (d+1)(d+1)-element subfamilies having a common point, and let ϕF(d)(m)\phi^{(d)}_\mathcal{F}(m) denote its ddth homological shatter function.

Kalai–Meshulam's fractional Helly conjecture. There exists a function β:(0,1)(0,1)\beta:(0,1)\to(0,1) such that, for every α>0\alpha>0 and every sufficiently large set system F\mathcal{F} in Rd\mathbb{R}^d satisfying

m0,ϕF(d)(m)Amk,\forall m\geq 0,\qquad \phi^{(d)}_\mathcal{F}(m)\leq A m^k,

if δF(d+1)α\delta_\mathcal{F}(d+1)\geq\alpha, then some β(α)F\beta(\alpha)|\mathcal{F}| members of F\mathcal{F} have a point in common.

This conjecture predicts a fractional Helly theorem for topological set systems whose homological shatter function has polynomial growth. The supplied passage presents it as one of two Kalai–Meshulam conjectures whose combination suggests this phenomenon; no resolution is given here.

Sources & referencesView supporting material

Primary source

Xavier Goaoc, Andreas F. Holmsen and Zuzana Patáková, “Intersection patterns in spaces with a forbidden homological minor”, arXiv:2103.09286 (2026).

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