The protagonist of this chapter should be the envy of any lover of travel. Apart from salesmen, tour guides, diplomats, and flight attendants, he may have spent more time in the air than anyone. He had no fixed occupation nor income but lived in hotels and ate in restaurants every day, his bills all paid for by others. He was a pure child prodigy with an unparalleled mind who later became the most prolific mathematician in history and made groundbreaking contributions to many diverse fields of mathematics. This was the Hungarian mathematician Paul Erdős, the subject of a biography entitled My Brain Is Open by Bruce Schechter, which I have read carefully in its Chinese translation for Shanghai Translation Press.