t-of-lists data type is not available,
      the information in the adjacency structure can also be constructed
      by a pair of vectors.  The first, the <b>adjacency list</b>, is
      simply the list of all the node neighbors of node 1, followed by
      those for node 2, and so on.  The <b>adjacency pointer</b> is a
      vector of length NV+1, which can be used to locate the data for
      a given node within the adjacency list.  In particular, the neighbors
      of node I are listed in the adjacency