I purchased this to compare it with the Top Class Problem Collection and have kept it unused. There is a stain on the bottom of the first-grade section, but it does not affect the inner pages. The "Thorough Understanding Edition" seems to be out of print, so please consider purchasing it soon if you are looking for it. As shown in the fifth photo, compared to the Top Class Problem Collection, this book has fewer "Top Class" problems and more "Standard/High Class" problems, specializing in building a more solid foundation. Each book is 1,386 yen including tax, and the two books are 2,772 yen. Immediate purchase and same-day shipping are available. No individual sales or price reductions.