The bijection between alcove covers and hypersimplicial decorated ordered set partitions

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Let nn be any positive integer and let A0A_0 be an alcove in the hypersimplex Δ2,n\Delta_{2,n}. Let PA0=(V,E)\mathcal{P}_{A_0}=(V,E) be the breadth-first search order of Γ2,n\Gamma_{2,n} rooted at A0A_0. For v∈Vv\in V, define

cover⁡(v)=#{u∈V∣u≺⋅v in PA0}\operatorname{cover}(v)=\#\{u\in V\mid u\prec\cdot v\text{ in }\mathcal{P}_{A_0}\}

to be the number of elements covered by vv. Bijection conjecture. The map ψ\psi is a bijection between

{v∈V∣cover⁡(v)=d}\{v\in V\mid \operatorname{cover}(v)=d\}

and the set of hypersimplicial decorated ordered set partitions of type (2,n)(2,n) with winding number dd. This would identify the breadth-first search structure of the alcove graph with the enumerative structure of hypersimplicial decorated ordered set partitions; the source does not provide resolution, so the claim remains open.

References

Primary source

Elisabeth Bullock and Yuhan Jiang, “The Ehrhart series of alcoved polytopes”, arXiv:2412.02787 (2025).

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