1. School of Computing, University of Leeds, Leeds, LS2 9JT, UK.
2. Mathematics Institute, University of Warwick, Coventry, CV4 7AL, UK.
3. Instituto de Ingeniería Matemática-CIMFAV, Universidad de Valparaiso, Valparaiso, Chile.
4. ArangoDB Inc., Berlin, Germany.
5. Department of Computer Science and Information Systems, Birkbeck University of London, London, UK.
6. Department of Computer Science, University of Liverpool, Liverpool, UK.