Waltraud Kahle is Associate Professor in the Mathematics Department of the Otto-von-Guericke University Magdeburg in Germany.
Sophie Mercier is Full Professor in the Laboratory of Mathematics and their Applications of the University of Pau and Pays de l’Adour in France.
Christian Paroissin is Associate Professor in the Laboratory of Mathematics and their Applications of the University of Pau and Pays de l’Adour in France.