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  1. Amazon.com: Difficult Crossword Puzzles: Books

  2. New York Times Seriously Hard Crossword Puzzles - amazon.com

  3. Amazon.com: Difficult Crossword Puzzle Books: Books

  4. Crossword Puzzle Books - Barnes & Noble

  5. The New York Times Seriously Hard Crossword Puzzles: 200 …

  6. The New York Times Seriously Hard Crossword Puzzles: 200 …

  7. The New York Times Hardest Crosswords Volume 15 - Macmillan

  8. The New York Times Awesome Hard Crossword Puzzles - Macmillan

  9. Hard Crossword Puzzles for Adults – Dylanna Press

  10. 5 Best Crossword Puzzle Books for Every Skill Level - RT Book …