Ecole Polytechnique, Palaiseau, France. waldispu@lix.polytechnique.fr|Ecole Polytechnique, Palaiseau, France. waldispu@lix.polytechnique.fr|Ecole Polytechnique, Palaiseau, France. waldispu@lix.polytechnique.fr|Ecole Polytechnique, Palaiseau, France. waldispu@lix.polytechnique.fr|Ecole Polytechnique, Palaiseau, France. waldispu@lix.polytechnique.fr|Ecole Polytechnique, Palaiseau, France. waldispu@lix.polytechnique.fr|Ecole Polytechnique, Palaiseau, France. waldispu@lix.polytechnique.fr|Ecole Polytechnique, Palaiseau, France. waldispu@lix.polytechnique.fr|Ecole Polytechnique, Palaiseau, France. waldispu@lix.polytechnique.fr|Ecole Polytechnique, Palaiseau, France. waldispu@lix.polytechnique.fr|Ecole Polytechnique, Palaiseau, France. waldispu@lix.polytechnique.fr|Ecole Polytechnique, Palaiseau, France. waldispu@lix.polytechnique.fr|Ecole Polytechnique, Palaiseau, France. waldispu@lix.polytechnique.fr|Ecole Polytechnique, Palaiseau, France. waldispu@lix.polytechnique.fr|Ecole Polytechnique, Palaiseau, France. waldispu@lix.polytechnique.fr|Ecole Polytechnique, Palaiseau, France. waldispu@lix.polytechnique.fr|Ecole Polytechnique, Palaiseau, France. waldispu@lix.polytechnique.fr|Ecole Polytechnique, Palaiseau, France. waldispu@lix.polytechnique.fr