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   Checks for valid HSA chordwiths
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   Form:
   yesNo = CwValid( ra, dec, er, g, ue )
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   Inputs
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   ra                     Right ascension
   dec                    Declination
   er                     Earth radius
   g                      Nominal cant angle
   ue                     Nadir vector

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   Outputs
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   yesNo                  0 if the chordwidth is invalid

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