Minimal-perimeter conjecture for ordinary reduced hyperbolic polygons

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Let P⊂H2P\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.

References

Primary source

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

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