1. School of Mathematics, University of the Witwatersrand, South Johannesburg, South Africa
2. INSA Centre Val de Loire, Univ. Orléans, LIFO EA 4022, Bourges, France
3. Faculty of Technology, Policy and Management, Delft University of Technology, the Netherlands and Department of Pure and Applied Mathematics, University of Johannesburg, South Africa
4. School of Business and Economics, Vrije Universiteit Amsterdam, Amsterdam, The Netherlands
5. Amsterdam Business School, University of Amsterdam, the Netherlands, College of Business and Economics, University of Johannesburg, Johannesburg, South Africa