Hard Series
This series is aimed at anyone looking for a tough challenge. The books are standalone and they can be used in any order. All hard puzzles have a full page to leave space for notes. Each book contains integrated solving tips, solutions in the book, and 110 puzzles:
- 10 medium II warmup
- 50 hard I
- 50 hard II
* Links on this page earn a small commission for directing traffic to Amazon without affecting purchase price.
