code: def add_root_match(self, lst_idx, root_idx):
          
          self.root_matches[lst_idx] = root_idx
          if lst_idx in self.in_result_idx:
              return
  
          self.not_in_result_root_match_idx.add(lst_idx)
docs: Adds a match for the elements avaialble at lst_idx and root_idx.