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

def are_equal(self, sp1, sp2):
        """
        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
        """
        set1 = set(sp1.elements)
        set2 = set(sp2.elements)
        return set1.issubset(set2) or set2.issubset(set1)