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A surface of revolution defined by Kepler. It consists of more 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
. It is the outside surface of a spindle
torus.
It is also a quartic surface given by Cartesian equation
(2)
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or
(3)
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