DeltCirc:

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   Find the angle between x and y. 

   This function is for subtracting numbers on a circle.

   Handle all input angles so that the solution is never greater
   than 2*pi.

   For example, DeltCirc( 2*pi, pi/6 )

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   Form:
   z = DeltCirc( x, y )
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   Inputs
   ------
   x                  Angle
   y                  Angle

   -------
   Outputs
   -------
   z                  Delta angle

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