1. Mathematics Department , Faculty of Sciences Semalalia , [ 107911]Cadi Ayyad University, Boulevard Prince Moulay Abdellah, P. O. Box 2390 , Marrakesh 40000 , Morocco
2. Mathematics Department , Faculty of Sciences , [ 226279]Chouaib Doukkali University, Route Ben Maachou, 24000 , El Jadida , Morocco