1. Higher Teachers’ Training College of the University of Maroua, P.O. Box 55, Maroua, Cameroon
2. Institute for Mathematics, Johannes Gutenberg University, Staudingerweg 9, 55099 Mainz, Germany
3. African Institute for Mathematical Sciences, P.O. Box 608 Limbe, Cameroon
4. Sub-regional Institute of Statistics and Applied Economics, P.O. Box 294 Yaoundé, Cameroon