Institution: | aSection of Mathematics, National Overseas Chinese Student University, Preparatory School, P.O. Box 1-1337, Linkou, Taiwan, 24499, Republic of China;bDepartment of Mathematics, National Central University, Chung-li, Taiwan, 32054, Republic of China;cDepartment of Mathematics, National Cheng-Kung University, Tainan, Taiwan, 70101, Republic of China |