code: def are_equal(self, sp1, sp2):
          
          set1 = set(sp1.elements)
          set2 = set(sp2.elements)
          return set1.issubset(set2) or set2.issubset(set1)
docs: True if there is some overlap in composition between the species
  
          Args:
              sp1: First species. A dict of {specie/element: amt} as per the
                  definition in Site and PeriodicSite.
              sp2: Second species. A dict of {specie/element: amt} as per the
                  definition in Site and PeriodicSite.
  
          Returns:
              True always