Admissibility criterion for regular spherical polygons

Let PP be a regular spherical polygon, and let its polar be the corresponding polar spherical polygon. Call PP admissible when it has the finite sentinel-set property: there is a finite subset SS of PP such that, for every spherical isometry TT, the polygons PP and TPTP intersect if and only if TPTP contains a point of SS or PP contains a point of TSTS.

Admissibility criterion. A regular spherical polygon is admissible if and only if the inner angle of its polar is at least

π/2.\pi/2.

The criterion would remove the extra side-length condition currently used in the proof for spherical triangles and is motivated by the necessity of the angle bound and by an extensive search for counterexamples. The statement remains open in the source.

Sources & referencesView supporting material

Primary source

Fernando Mário de Oliveira Filho, Andreas Spomer and Frank Vallentin, “Bounding the density of spherical polygon packings”, arXiv:2604.21451 (2026).

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