docs: def _get_elem_names(self):
          """ returns for one cycle an element name dictionary."""
  
          import nuutils as u
  
          # provide library for Z versus element names, and Z for elements
          #element_name = self.se.elements
          element_name = self.elements_names
          u.give_zip_element_z_and_names(element_name)
          self.z_of_element_name = u.index_z_for_elements