1. Department of Mathematical Analysis, Faculty of Science, Palacký University, Tomkova 40, Olomouc 779 00, Czech Republic
2. Department of Engineering Sciences and Methods, University of Modena and Reggio Emilia, Via Fogliani 1, Reggio Emilia 42100, Italy
3. Department of Mathematics and Informatics, University of Udine, Viadelle Scienze 206, Udine 33100, Italy