Yotsuya Otsuka Yosyu Series Arithmetic, Year 4 Most Difficult Problem Collection, Volumes 1 & 2 Volume 1 only, with check marks where mistakes were made, and with the owner's name written. Volume 2 has no writing or name. Since these were used at a cram school, I will sell them to someone who doesn't mind the details. For students who will finish in 2026.