Book excerpt: This popular, even more challenging variant of sudoku is for true puzzle warriors! Each one consists of FIVE sudoku grids arranged in an X-shaped array, with overlapping corners. No grid can be solved on its own; to complete the entire puzzle, players have to work on several grids at once, making their way to overlapping areas and constantly searching for new clues. While regular sudoku-solving techniques provide the starting point, the game's more complicated than that. Because the overlapping areas belong to two different grids, they must comply with the rules of both simultaneously. That changes the puzzle's underlying logic...and makes these sudokus more fun for the serious fan. An introduction, with a sample puzzle, shows all the strategies.