code: def subtract(self):
          
  
          if self.moc is None:
              raise CommandError('No MOC information present for subtraction')
  
          filename = self.params.pop()
          self.moc -= MOC(filename=filename)
docs: Subtract the given MOC from the running MOC.
  
          This command takes the name of a MOC file to be subtracted from the
          running MOC.
  
          ::
  
              pymoctool a.fits --subtract b.fits --output difference.fits