Affiliation: | Department of Mathematics, National Central University, Chung-Li, 32054 Taiwan, Republic of China Fu-Hsiang Wong ; Department of Mathematics and Science, National Taipei Teacher's College, 134, Ho Ping e. Rd. Sec. 2, Taipei 10659, Taiwan, Republic of China Cheh-Chih Yeh ; Department of Mathematics, National Central University, Chung-Li, 32054 Taiwan, Republic of China |