Religious language is often employed by mathematicians, even among those who aren’t particularly pious. Paul Erdős, a famously prolific mathematician who was fond of referring to God as the Supreme Fascist, also liked to speak of “The Book” that God keeps in which all of the most beautiful proofs are recorded. He once quipped, “You don’t have to believe in God, but you should believe in the Book.” This unseen Book was an apparent nod to the timelessness of mathematical ideas, whose existence and persistence parallels the eternal nature that some expect of divine truths.