1. Departamento de Matemáticas, Universidad de Cádiz , Cádiz, España.
2. CMCC, Universidade Federal do ABC , Santo André, Brasil.
3. CeBER-Centre for Business and Economics Research, University of Coimbra , Coimbra, Portugal.
4. CMUC-Centre for Mathematics, University of Coimbra , Coimbra, Portugal.
5. FEUC, Universidade de Coimbra , Coimbra, Portugal.