Sudoku X - 200 Hard to Master Puzzles 9x9 (Volume 15)

Sudoku X (also known as "Diagonal Sudoku") is a placement puzzle. In this sudokus main diagonals also contain the digits 1 through 9. About Book
This book introduces you to the amazing world of Sudoku X puzzles.
It will help you understand the rules of this puzzle.
This book is perfect for players of all ages.
You will find 200 exciting puzzles, for professionals. HOW TO PLAY
It is a 9x9 grid, partially divided by black cells into compartments. The puzzle is most frequently a 9x9 grid made up of 3x3 subgrids (called "regions"). Some cells already contain numbers, known as "givens". The goal is to fill in the empty cells, one number in each, so that each column, row, and region contains the numbers 1 through 9 exactly once. Main diagonals also contain the digits 1 through 9. Each number in the solution therefore occurs only once in each of three "directions".