1. Departament de Física i Enginyeria Nuclear, Universitat Politècnica de Catalunya, Campus Nord, Módul B4, 08034 Barcelona, Spain
2. Dipartimento di Fisica, Università "La Sapienza" and SMC-INFM, P. le A. Moro 2, 00185 Roma, Italy
3. Complex Networks Lagrange Laboratory, ISI Foundation, Viale S. Severo 65, 10133, Torino, Italy
4. VUB AI Lab, Brussels, Belgium
5. Sony Computer Science Laboratory, Paris, France