1. Center for Research and Development in Mathematics and Applications (CIDMA), Department of Mathematics, University of Aveiro, 3810-193 Aveiro, Portugal
2. Department of Mathematics, University of Djelfa, Djelfa 17000, Algeria
3. Department of Mathematics, ISCTE—Instituto Universitário de Lisboa, 1649-026 Lisbon, Portugal
4. Research Center in Exact Sciences (CICE), Faculty of Sciences and Technology (FCT), University of Cape Verde (Uni-CV), Praia 7943-010, Cape Verde