Affiliation: | aDepartment of Economy and Management, College of Business Administration, Polytechnic Institute of Setúbal, Portugal;bDepartment of Mathematics, University of Èvora, Colégio Luis António Verney, Rua Romão Ramalho 59, 7002 Èvora, Portugal;cDepartment of Mathematics, FCT, Nova University of Lisbon, Quinta da Torre, 2825 Monte da Caparica, Portugal |