1. Department of Mathematics and Computer Science, Faculty of Science, University of Ngaoundéré, Ngaoundere, Cameroon
2. Department of Computer Engineering, University Institute of Technology, University of Ngaoundéré, Ngaoundere, Cameroon
3. Faculty of Engineering and Computer Science, Osnabrück University of Applied Sciences, Osnabrück, Germany
4. Department of Mathematics, Rhodes University, Grahamstown, South Africa