static BufferedImage tilesToImage_twoLevelList(LL<BufferedImage> tiles) {
  if (empty(tiles)) null;
  int columns = maxLength(tiles);
  int rows = l(tiles);
  int tw = first(first(tiles)).getWidth(), th = first(first(tiles)).getHeight();
  int w = tw*columns, h = th*rows;
  BufferedImage img = newBufferedImage(w, h);
  
  for y to rows:
    for x to columns:
      copyBufferedImage(get(tiles.get(y), x), img, x*tw, y*th);
  ret img;
}