Difficult Sudoku Book: 200 Difficult Sudoku Puzzles

This is a book of difficult Sudoku puzzles.Some of the puzzles require you to applyadvanced Sudoku solving techniques suchas X-Wing or Swordfish. However, all puzzles can be solved withoutguessing and have one solution only. If you need help, you can always peek at the solutions. Remember: do not guess! The book is small in size but the numbers areprinted in large font, easy to read. All puzzles in this book are NEW, previously unpublished!