Uniform surface conjecture for exterior algebraic shifting

Let SgS_g be a fixed orientable surface of genus gg, and let Un(Sg)U_n(S_g) denote its uniform random triangulation with nn vertices. Let Δex\Delta^{ex} denote exterior algebraic shifting over a fixed field, and let Δ(Sg,n)\Delta(S_g,n) be the corresponding homology lex-segment complex.

Uniform surface conjecture. For every fixed genus gg, a.a.s.,

Δex(Un(Sg))=Δ(Sg,n).\Delta^{ex}(U_n(S_g))=\Delta(S_g,n).

This would show that the exterior shifting of a uniform triangulation of a fixed orientable surface is a homology lex-segment and, in particular, that Un(Sg)U_n(S_g) is a.a.s. K6K_6-free. The statement is not known; local neighborhoods of almost every vertex are known to be a.a.s. planar.

Sources & referencesView supporting material

Primary source

Denys Bulavka, Eran Nevo and Yuval Peled, “The typical algebraic shifting of a surface”, arXiv:2509.26525 (2025).

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