The representability bound for simplicial complexes with bounded Leray number

Let XX be a simplicial complex with nn vertices, and let h(X)h(X) denote its Leray number.

Representability bound conjecture. If h(X)dh(X)\leq d for d1d\geq 1, then

rep(X)dnd+1.\operatorname{rep}(X)\leq \left\lfloor\frac{dn}{d+1}\right\rfloor.

Moreover, equality rep(X)=dnd+1\operatorname{rep}(X)=\frac{dn}{d+1} holds if and only if the missing faces of XX consist of nd+1\frac{n}{d+1} pairwise disjoint sets of size d+1d+1.

This conjecture extends the sharp graph case and predicts both a universal upper bound and its extremal complexes. Its resolution would strengthen the known relationship between representability and Leray number; the general case remains open.

Sources & referencesView supporting material

Primary source

Alan Lew, “Representability and boxicity of simplicial complexes”, arXiv:2008.09997 (2020).

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