Affiliation: | 1. Department of Mathematics, Institute of Mathematical Research, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia;2. School of Mathematical Sciences, Faculty of Science and Technology, Universiti Kebangsaan Malaysia, 43600 UKM Bangi, Selangor, Malaysia;3. Faculty of Mathematics, University of Cluj, R-3400 Cluj, CP 253, Romania |