1. Department of Mathematics—City, University of London—Northampton Square, London EC1V 0HB, UK
2. Max Planck Institute for Evolutionary Anthropology, Department of Human Behaviour, Ecology and Culture, Leipzig, Germany
3. Departament de Física, Universitat Politècnica de Catalunya, Campus Nord B4, 08034 Barcelona, Spain
4. UCL Centre for Blockchain Technologies, University College London, London, UK