Sudoku Puzzle Book: The Ultimate Sudoku Challenge

WHAT IS A SUDOKU PUZZLE A classic sudoku puzzle is made up of a 9-by-9 grid with nine 3-by-3 sub-grids called boxes. There are 9 rows, 9 columns and 9 boxes in every puzzle. The object of the game is to fill all squares in the grid with the correct number. The rules are: -Every row, column and box must contain all the digits 1 to 9. -Each number can only appear once in every row, column or box. Every puzzle has only one correct solution! There are 50 difficult level puzzles - only for those...