1. Department MATESCO, Universidad de Cantabria , Avda. Los Castros s/n, 39005 Santander, Spain
2. Department of Mathematics and Systems Analysis, Aalto University , P.O. Box 11100, FI-00076 Aalto, Finland
3. Department of Computer Science, KU Leuven, Celestijnenlaan 200A , B-3001 Leuven, Belgium