Affiliation: | 1.Department of Mathematics, Faculty of Science, University of Zagreb, Bijeni?ka cesta 30, 10000, Zagreb, Croatia ;2.School of Mathematics, University of the Witwatersrand, Private Bag X3, Wits, 2050, South Africa ;3.Research Group in Algebraic Structures and Applications, King Abdulaziz University, Jeddah, Saudi Arabia ;4.Department of Mathematics, Faculty of Sciences, University of Ostrava, 30 Dubna 22, 701 03, Ostrava 1, Czech Republic ; |