1. Institute for New Economic Thinking at the Oxford Martin School, University of Oxford, Oxford OX2 6ED, UK.
2. Mathematical Institute, University of Oxford, Oxford OX1 3LP, UK.
3. Department for Business Studies and Economics, University of Bremen, 28359 Bremen, Germany.
4. Computer Science Department, University of Oxford, Oxford OX1 3QD, UK.
5. Santa Fe Institute, Santa Fe, NM 87501, USA.