This book wouldn't have existed without Raffaella Lops.
I would like to thank, in no particular order, Antonio Franchini, Joy Terekiev, Mario Desiati, Giulia Ichino, Laura Cerutti, Cecilia Giordano, my parents, Giorgio Mila, Roberto Castello, Emiliano Amato, Pietro Grossi, and Nella Re Rebaudengo. Each of them knows why.