Alain Badiou was once seated amongst the public in a room where I was delivering a talk, when his cellphone (which, to add insult to injury, was mine -- I had lent it to him) all of a sudden started to ring. Instead of turning it off, he gently interrupted me and asked me if I could talk more softly, so that he could hear his interlocutor more clearly . . . If this was not an act of true friendship, I do not know what friendship is. So, this book is dedicated to Alain Badiou.