Hard Sudoku Book: 200 Difficult Sudoku Puzzles (Sudoku puzzle books)

This is a book of difficult Sudoku puzzles. Some of the puzzles require you to apply advanced Sudoku solving techniques such as X-Wing or Swordfish.
However, all puzzles can be solved without guessing 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 are printed in large font, easy to read.

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