Author/Authors :
Massar، M. نويسنده Department of Mathematics, University Mohamed I, Oujda, Morocco , , Hssini، E. M. نويسنده Department of Mathematics, University Mohamed I, Oujda, Morocco , , Tsouli، N. نويسنده Department of Mathematics, University Mohamed I, Oujda, Morocco , , Talbi، M. نويسنده CRMEF, Oujda, Morocco ,