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Umbilic Point


An umbilic point, also called simply an umbilic, is a point on a surface at which the curvature is the same in any direction.

Carathéodory's conjecture predicts at least two umbilic points on every closed strictly convex smooth surface in R^3. Loewner's conjecture gives the related local index bound. Ando and Umehara (2026) reported a smooth non-real-analytic strictly convex closed surface with exactly one umbilic point of index 2. Independent verification of the full construction has not been established. Ando and Umehara (2026) report AI assistance with the mathematical construction.


See also

Curvature

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References

Ando, N. and Umehara, M. "A Simple Construction of Smooth Counterexamples to the Loewner and Carathéodory Conjectures." 25 Oct 2026. https://arxiv.org/abs/2610.34036.

Referenced on Wolfram|Alpha

Umbilic Point

Cite this as:

Weisstein, Eric W. "Umbilic Point." From MathWorld--A Wolfram Resource. https://mathworld.wolfram.com/UmbilicPoint.html

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