a1 Department of Mathematics, University of Pisa, Piazza Pontecorvo 5, 56127 Pisa, Italy email: milani@dm.unipi.it
For conclusions, the traditional approach in IAU meetings is to have a highlights speech, in which the most important points of the meeting are stressed. After consulting with the co-chairs of the Scientific Organizing Committee, I decided I would rather discuss the spirit of this meeting from a more conceptual point of view.