code: def _proc_dihedral(self):
          
          main_axis, rot = max(self.rot_sym, key=lambda v: v[1])
          self.sch_symbol = "D{}".format(rot)
          mirror_type = self._find_mirror(main_axis)
          if mirror_type == "h":
              self.sch_symbol += "h"
          elif not mirror_type == "":
              self.sch_symbol += "d"
docs: Handles dihedral group molecules, i.e those with intersecting R2 axes
          and a main axis.