[1] Inst Politecn Nacl, ESIME Zacatenco, Mexico City 07738, DF, Mexico
[2] Univ Holguin, Fac Informat & Matemat, Holguin 80100, Cuba
[3] Inst Tecnol Autonomo Mexico, Dept Matemat, Rio Hondo 1,Col Progreso Tizapan, Mexico City 01080, DF, Mexico
[4] Izmir Univ Econ, Fac Sci & Literature, Dept Math, TR-35330 Izmir, Turkey