1. Centre for Complexity Science, Department of Mathematics, Imperial College London, London SW72AZ, UK
2. Division of Mathematics and Computer Science, Krea University, Sri City, Andhra Pradesh 517646, India
3. Mansueto Institute for Urban Innovation, Department of Ecology and Evolution, Department of Sociology, University of Chicago, Chicago, IL 60637, USA
4. Santa Fe Institute, Santa Fe, NM 87501, USA