Diagonal Sudoku: 200 Puzzles With An X

Diagonal Sudoku (Sudoku X) puzzles add another twist to your favorite game: both diagonals must contain all digits from 1 to 9 precisely once. This additional rule forces you to use new solving methods which are explained in the introduction. The books contains 200 puzzles split into 5 levels of difficulty. None of the puzzles are too easy and they cannot be solved without using the "X" rule.