Bull. Korean Math. Soc. 2015; 52(6): 2001-2010
Printed November 30, 2015
https://doi.org/10.4134/BKMS.2015.52.6.2001
Copyright © The Korean Mathematical Society.
Dae San Kim and Taekyun Kim
Sogang University, Kwangwoon University
© 2022. The Korean Mathematical Society. Powered by INFOrang Co., Ltd