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A generalization of the ring Torus produced by stretching or compressing in the 
 direction.  It is
given by the parametric equations
See also Torus
References
Gray, A.  ``Tori.''  §11.4 in Modern Differential Geometry of Curves and Surfaces.
  Boca Raton, FL: CRC Press, pp. 218-220, 1993.