litongx2007@163.com
zchui@sdu.edu.cn
blanka.baculikova@tuke.sk
jozef.dzurina@tuke.sk
© 2012 Tongxing Li, Chenghui Zhang, Blanka Baculíková, Jozef Džurina, published by Slovak Academy of Sciences, Mathematical InstituteThis work is licensed under the Creative Commons License.