Every day, tens of millions of sudoku fans get out their pencils and attack the latest 9x9 puzzle in their daily newspaper. But a huge percentage of those fans are starting to feel they8217;ve mastered standard sudoku and are hungry for tougher challenges. Well, here they are: sudoku on overlapping grids, sudoku with unusually shaped areas instead of 3x3 squares, sudoku with special rules, and even extra-large sudoku for an extra-fun solving experience.160; Thanks to Conceptis Ltd., the world8217;s leading supplier of puzzles to newspapers and magazines, sudoku8217;s horizons have just opened up beyond the wildest dreams of its most devoted solvers.