TOSHIKI MABUCHI is Professor of Mathematics at the College of General Education, Osaka University, Japan. The author or coauthor of numerous journal articles and book chapters and coeditor of the Osaka Journal of Mathematics, he is a member of the Mathematical Society of Japan. Dr. Mabuchi received the Ph.D. degree (1977) in mathematics from the University of California, Berkeley, and the Ph.D. degree (1983) in mathematics from Osaka University, Japan. SHIGERU MUKAI is Professor of Mathematics at the School of Science, Nagoya University, Japan. The author or coauthor of many journal articles and book chapters and coeditor of the Nagoya Mathematical Journal, he is a member of the Mathematical Society of Japan. Dr. Mukai received the Ph.D. degree (1982) in mathematics from Kyoto University, Japan.