/* Determine if a graph is bipartite or not.
 */
BEG_G{
  int vc, c, color[node_t];
  node_t v;
  edge_t e;
  $tvtype = TV_dfs;
  $tvroot = fstnode($);
}
N{
  if ($tvedge == NULL)
    color[$] = 1;
  if (color[$] == 1)
    c = 2;
  else
    c = 1;
  for (e = fstedge($); e; e = nxtedge(e,$)) {
    v = opp(e,$);
    vc = color[v];
    if (vc == 0)
      color[v] = c;
    else if (vc != c) {
      printf(2, "Not bipartite\n");
      exit(1);
    }
  }
}