Solved and Unsolved Problems

[摘要] With this opportunity, I would like to express my deepest thanksto Professor Martin Raussen, who appointed me as a member ofthe Editorial Board of the Newsletter of the EMS in charge of theproblem corner in 2005. I would also like to express my gratitude toProfessor Krzysztof Ciesielski for proposing in 2004 that I write anarticle in the Newsletter of the EMS, which subsequently initiatedmy communication with Martin Raussen, with whom I have had awonderful and productive collaboration. I note that editors generally serve for four years and I feel deeply honoured that my membership as the problem column editor has lasted for more than 10years. Thus, I wish to express my sincere thanks to Professors Vicente Munoz and Lucia Di Vizio, who served as Editors-in-Chiefafter Martin Raussen; I continued to have a wonderful collaborationwith them.