The face-map conjecture for local-model toric strata

From papers

Let AdmG({μ}){\rm Adm}^{\mathcal G}(\{\mu\}) be the admissible set and let Δ|\Delta| be the divisor map from this poset to the face poset F(σG,μ){\mathscr F}(\sigma_{{\mathcal G},\mu}). For wAdm({μ})w\in{\rm Adm}(\{\mu\}), define

Λ(w)={μˉΛ{μ}wtμˉ}.\Lambda(w)=\{\bar\mu'\in\Lambda_{\{\mu\}}\mid w\leq t^{\bar\mu'}\}.

Let Δf(w)|\Delta|^{\rm f}(w) be the smallest face of σG,μ\sigma_{{\mathcal G},\mu} containing the extremal rays corresponding to the elements of Λ(w)\Lambda(w). The face-map conjecture. The map Δ|\Delta| coincides with the map Δf|\Delta|^{\rm f}. This gives a purely combinatorial description of the divisor map; the source does not state a resolution or further cases in which it is known.

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Sources & referencesView supporting material

Primary source

Georgios Pappas and Michael Rapoport, “Toric schemes and integral models for Shimura varieties with Γ_1(p)-type level”, arXiv:2602.23245 (2026).

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