1  void
       2  foo (int n, int m)
       3  {
       4    if (m == 0)
       5      exit (0);
       6    else if (n != 0)
       7      abort ();
       8    else
       9      foo (n++, m - 1);
      10  }
      11   
      12  int
      13  main (void)
      14  {
      15    foo (0, 4);
      16  }