code: def _proc_cyclic(self):
          
          main_axis, rot = max(self.rot_sym, key=lambda v: v[1])
          self.sch_symbol = "C{}".format(rot)
          mirror_type = self._find_mirror(main_axis)
          if mirror_type == "h":
              self.sch_symbol += "h"
          elif mirror_type == "v":
              self.sch_symbol += "v"
          elif mirror_type == "":
              if self.is_valid_op(SymmOp.rotoreflection(main_axis,
                                                        angle=180 / rot)):
                  self.sch_symbol = "S{}".format(2 * rot)
docs: Handles cyclic group molecules.