GR Sudoku Zorzos: Volume I

In this book you can play and solve HARD Sudoku and see the solution at the end. According to Wiki: Sudoku is a logic-based, combinatorial number-placement puzzle. The objective is to fill a 9×9 grid with digits so that each column, each row, and each of the nine 3×3 sub-grids that compose the grid (also called boxes, blocks, regions or sub-squares) contains all of the digits from 1 to 9. The puzzle setter provides a partially completed grid, which typically has a unique solution.