code: def traverse(self, edge):
          
          query = self.statement
          rel, dst = edge.rel, edge.dst
          statement, params = (
              SQL.compound_fwd_query(query, rel) if dst is None else
              SQL.compound_inv_query(query, rel, dst)
          )
          return self.derived(statement, params, replace=True)
docs: Traverse the graph, and selecting the destination
          nodes for a particular relation that the selected
          nodes are a source of, i.e. select the friends of
          my friends. You can traverse indefinitely.
  
          :param edge: The edge query. If the edge's
              destination node is specified then the source
              nodes will be selected.