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A Ruled Surface  is a normal developable of a curve
 is a normal developable of a curve  if
 if  can be parameterized by
 can be parameterized by
 , where N is the Normal Vector.
, where N is the Normal Vector.
See also Binormal Developable, Tangent Developable
References
Gray, A.  ``Developables.''  §17.6 in Modern Differential Geometry of Curves and Surfaces.
  Boca Raton, FL: CRC Press, pp. 352-354, 1993.