Minimal-perimeter conjecture for ordinary reduced hyperbolic polygons

Let PH2P\subset H^2 be an ordinary reduced nn-gon of minimal width ww. Let P~\widetilde{P} denote the regular ordinary reduced nn-gon of width ww, and write perim(P)\operatorname{perim}(P) for the perimeter of PP. Minimal-perimeter conjecture.

perim(P)perim(P~)\operatorname{perim}(P)\leq\operatorname{perim}(\widetilde{P})

with equality if and only if PP is regular. The conjecture proposes that, among ordinary reduced hyperbolic nn-gons with a fixed minimal width, the regular polygon has maximal perimeter; the surrounding discussion explains that the usual Jensen-inequality argument for the Euclidean and spherical cases does not apply in the hyperbolic plane.

Sources & referencesView supporting material

Primary source

Ádám Sagmeister, “On the perimeter, diameter and circumradius of ordinary hyperbolic reduced polygons”, arXiv:2410.03666 (2025).

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