The corkscrew surface, sometimes also called the twisted sphere (Gray 1997, p. 477), is a surface obtained by extending a sphere along a diameter and then twisting. It can be specified parametrically as
(1)
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(2)
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(3)
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The coefficients of the first fundamental form are
(4)
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(5)
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(6)
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and those of the second fundamental form are
(7)
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(8)
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(9)
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The Gaussian and mean curvatures are
(10)
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(11)
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