1. Department of Computing Science, Umeå University , Umeå 90187, Sweden
2. Department of Informatics, King’s College London , London WC2R 2, UK, and Department of Computer Science, University of Luxembourg, Esch-sur-Alzette 4364, Luxembourg
3. Department of Law, European University Institute , Florence 50139, Italy, and Department of Legal Studies, Università di Bologna, Bologna 40126, Italy