Book excerpt: 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 they’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. Thanks to Conceptis Ltd., the world’s leading supplier of puzzles to newspapers and magazines, sudoku’s horizons have just opened up beyond the wildest dreams of its most devoted solvers.