digraph gag {
  one_mod_3 -> two_mod_3;
  zero_mod_3;
  two_mod_3 -> zero_mod_3;
  zero_mod_3 -> one_mod_3;
  one_mod_3 -> tree_3n_plus_2;
  tree_3n_plus_2;
  tree_3n_plus_2 -> tree_3n_plus_2;
  tree_3n_plus_2 -> tree_3n_plus_2;
}
