1. Centrum Wiskunde and Informatica, Scientific Computing, Science Park 123, 1098 XG Amsterdam, The Netherlands
2. Centrum Wiskunde and Informatica, Scientific Computing, Science Park 123, 1098 XG Amsterdam, The NetherlandsbUniversity of Antwerp, iMinds-Vision Lab, Universiteitsplein 1, Building N, 2610 Wilrijk, BelgiumcLeiden University, Mathematical Institute, Niels