code: def link(self, node, hyperedge):
          
          if (hyperedge not in self.node_links[node]):
              self.edge_links[hyperedge].append(node)
              self.node_links[node].append(hyperedge)
              self.graph.add_edge(((node,'n'), (hyperedge,'h')))
          else:
              raise AdditionError("Link (%s, %s) already in graph" % (node, hyperedge))
docs: Link given node and hyperedge.
  
          @type  node: node
          @param node: Node.
  
          @type  hyperedge: node
          @param hyperedge: Hyperedge.