code: def _fix_labels(self):
          
          for s in self.systems:
              mag0 = np.inf
              n0 = None
              for n in self.get_system(s):
                  if isinstance(n.parent, DummyObsNode):
                      continue
                  mag, _ = n.parent.value
                  if mag < mag0:
                       mag0 = mag
                       n0 = n
  
              # If brightest is not tag _0, then switch them.
              if n0 is not None and n0.tag != 0:
                  n_other = self.get_leaf('{}_{}'.format(s,0))
                  n_other.tag = n0.tag
                  n0.tag = 0
docs: For each system, make sure tag _0 is the brightest, and make sure
          system 0 contains the brightest star in the highest-resolution image