Introduction:
Kuen's surface has the same constant negative Gaussian
curvature as the sphere and pseudosphere.
It is quite complicated, as a front-back coloring reveals:

Definition:

Properties:
Infinitesimal Area:
The infinitesimal area of a patch on the surface is given by

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Gaussian Curvature:

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Gaussian curvature of the
surface.
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Surface colored by Gaussian
curvature.
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Mean Curvature:

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Mean curvature of the surface.
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Surface colored by Mean
curvature.
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