 I would like to thank Karine Chemla for having encouraged me to think about this topic and Andrea Albrecht, Enrico Bombieri, Leo Corry, Jacques Dubucs, Jean Gayon, James Hamilton, Robert MacPherson, Marco Panza, Chris Pincock, Martin Powell, Erich Reck, and Jamie Tappenden for useful comments on a previous draft and for their help in tracking down relevant literature. This essay is dedicated to Alessandra Schiaffonati, in memory of her inimitable style.