code: def links(self, obj):
          
          if obj in self.edge_links:
              return self.edge_links[obj]
          else:
              return self.node_links[obj]
docs: Return all nodes connected by the given hyperedge or all hyperedges
          connected to the given hypernode.
          
          @type  obj: hyperedge
          @param obj: Object identifier.
          
          @rtype:  list
          @return: List of node objects linked to the given hyperedge.