1. CMUC, Department of Mathematics, University of Coimbra, Coimbra, Portugal
2. Department of Mathematics, Pontifical Catholic University of Rio de Janeiro – PUC-Rio, Gávea, Rio de Janeiro-RJ, Brazil
3. Instituto Superior Técnico, Department of Mathematics, University of Lisbon, Lisbon, Portugal
4. Department of Mathematics University of Central Florida, Orlando, FL, USA