A coordinate system which is similar to bispherical coordinates but having fourth-degree surfaces instead of second-degree surfaces for constant . The coordinates are given by the transformation equations
(1)
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(2)
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(3)
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where
(4)
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, , , and , , and are Jacobi elliptic functions. Surfaces of constant are given by the bicyclides
(5)
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surfaces of constant by the cyclides of rotation
(6)
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and surfaces of constant by the half-planes
(7)
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