Affiliation: | (1) LIX, école Polytechnique, 91128 Palaiseau, France gaudry@lix.polytechnique.fr, FR;(2) School of Mathematics and Statistics F07, University of Sydney, Sydney, NSW 2006, Australia florian@maths.usyd.edu.au, AU;(3) Computer Science Department, University of Bristol, Woodland Road, Bristol BS8 1UB, England nigel@cs.bris.ac.uk, UK |