1Department of Mathematics, National Changhua University of Education, Changhua 500, Taiwan. maiblian@cc.ncue.edu.tw|1Department of Mathematics, National Changhua University of Education, Changhua 500, Taiwan. maiblian@cc.ncue.edu.tw|1Department of Mathematics, National Changhua University of Education, Changhua 500, Taiwan. maiblian@cc.ncue.edu.tw|1Department of Mathematics, National Changhua University of Education, Changhua 500, Taiwan. maiblian@cc.ncue.edu.tw|1Department of Mathematics, National Changhua University of Education, Changhua 500, Taiwan. maiblian@cc.ncue.edu.tw|1Department of Mathematics, National Changhua University of Education, Changhua 500, Taiwan. maiblian@cc.ncue.edu.tw