1. School of Mathematical and Physical Science, University of Newcastle, Callaghan, NSW 2308, Australia
2. School of Mathematical and Physical Science, University of Newcastle, Callaghan, NSW 2308, Australia; and H. Milton Stewart School of Industrial and Systems Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332
3. SK Innovation, Seoul, South Korea 03188
4. Constraint Technologies International, Melbourne, VIC 3000, Australia