new_contents: def lattice_path(grid_size):
    if grid_size == [0, 0]:
      return 1
    paths = 0
    if grid_size[0] > 0:
      print grid_size
      paths += lattice_path([grid_size[0] - 1, grid_size[1]])
    if grid_size[1] > 0:
      print grid_size
      paths += lattice_path([grid_size[0], grid_size[1] - 1])
    return paths
  
  if __name__ == '__main__':
    print lattice_path([2, 2])
  
subject: solve problem 15