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A surface of revolution defined by Kepler. It consists of less than half of a circular arc rotated about an axis passing through the endpoints of the arc. The equations of the upper and lower boundaries in the plane are
(1)
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for and . The cross section of a lemon is a lens. The lemon is the inside surface of a spindle torus. The American football is shaped like a lemon.
Two other lemon-shaped surfaces are given by the sextic surface
(2)
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called the "citrus" (or zitrus) surface by Hauser (left figure), and the sextic surface
(3)
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whose upper and lower portions resemble two halves of a lemon, called the limão surface by Hauser (right figure).
The citrus surface had bounding box , centroid at , volume
(4)
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and a moment of inertia tensor
(5)
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for a uniform density solid citrus with mass .