1 Faculty of Mathematics and Computer Science, Nicolaus Copernicus University, 87-100 Toruń, Poland, and Faculty of Mathematics, Informatics and Mechanics University of Warsaw, 02-097 Warsaw, Poland wrejchel@gmail.com.
2 School of Mathematics and Statistics, Huazhong University of Science and Technology, Wuhan 430074, China hongli@mail.hust.edu.cn.
3 School of Mathematics and Statistics, Huazhong University of Science and Technology, Wuhan 430074, China rcbrcb2004@163.com.
4 Faculty of Mathematics and Statistics, Hubei University, Wuhan 430062, China lilq@hubu.edu.cn.
This note corrects an error in the proof of corollary 1 of Li et al. ( 2014 ). The original claim of the contraction principle in appendix D of Li et al. no longer holds.