Around 1956: "My next task was to prepare my course. Since none of the textbooks known to me was satisfactory, I resorted to the maieutic method that Plato had attributed to Socrates. My lectures consisted essentially in questions that I distributed beforehand to the students, and an abstract of the research that they had prompted. I wrote each question on a 6 × 8 card. I had adopted this procedure a few years earlier for my own work, so I did not start from scratch. Eventually I filled several hundreds of such cards, classed them by subject, and placed them in boxes. When a box filled up, it was time to write an article or a book chapter. The boxes complemented my hanging-files cabinet, containing sketches of papers, some of them aborted, as well as some letters." (p. 129)