code: def is_subgroup(self, supergroup):
          
          warnings.warn("This is not fully functional. Only trivial subsets are tested right now. ")
          return set(self.symmetry_ops).issubset(supergroup.symmetry_ops)
docs: True if this group is a subgroup of the supplied group.
  
          Args:
              supergroup (SymmetryGroup): Supergroup to test.
  
          Returns:
              True if this group is a subgroup of the supplied group.