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This book is very good! I've been obsessed with Sudoku recently, and this book provides a lot of Sudoku problems of varying difficulty, allowing me to constantly challenge myself. I especially like the problem-solving methods and techniques introduced in the book. They allow me to solve Sudoku problems faster and also allow me to understand the rules and logic of Sudoku more deeply. However, there are also things I don't like, that is, some of the questions are too difficult and it took me a long time to solve them, which made me a little frustrated. However, this also makes me more motivated to challenge more difficult Sudoku problems. Overall, this is a very good Sudoku book, recommended to all friends who like Sudoku!