Beyond Black Belt Sudoku: If you have to ask, it's too hard for you. (Martial Arts Puzzles Series) / Longo, Frank

For diehards only! These incredibly difficult puzzles are handcrafted for the sudoku warrior who dares to go where other solvers fear to tread. So, if you're armed with the highest-level strategies, get ready for the most satisfying fight your life.

It's the most challenging sudoku book we've ever published!