docs: def rename_node(self, prefix):
          """
          Rename AMR graph nodes to prefix + node_index to avoid nodes with the same name in two different AMRs.
  
          """
          node_map_dict = {}
          # map each node to its new name (e.g. "a1")
          for i in range(0, len(self.nodes)):
              node_map_dict[self.nodes[i]] = prefix + str(i)
          # update node name
          for i, v in enumerate(self.nodes):
              self.nodes[i] = node_map_dict[v]
          # update node name in relations
          for node_relations in self.relations:
              for i, l in enumerate(node_relations):
                  node_relations[i][1] = node_map_dict[l[1]]