1. Department of Mathematical Sciences, University of Delaware, Newark, DE 19716, USA. nhbong@udel.edu
2. Department of Applied Mathematics and Informatics, Technical University, Košice, Slovak Republic. martin.baca@tuke.sk, andrea.fenovcikova@tuke.sk
3. Department of Mathematics, University of Indonesia, Kampus UI Depok, Depok 16424, Indonesia. kiki@sci.ui.ac.id
4. Department of Applied Mathematics, Tunghai University, Taichung, Taiwan, ROC. wang@go.thu.edu.tw