Instruct: Classify Amazon reviews into positive or negative sentiment
Query: Challenging at first, yet gets curiously easier

The first time I read this book, I found the puzzles very challenging; some, in fact, were very difficult. I re-read the book a few weeks later and found, however, the puzzles were not as difficult as I recalled. I was really disappointed by my third and fourth reading - the puzzles were not challenging at all!A good book overall, but either I got a lot smarter during the three months I read and re-reread this book (I been taking flaxseed oil daily, which may explain this), or the publishers have devised some way to revise the book while it is in my possession.