Last night, my four-year-old daughter Anna asked me this question: “What’s the number right before infinity?” Somebody (not me) had told her about infinity, and she has obviously been thinking about it. How would you answer that question? I thought about it and decided to just answer correctly: the number right before infinity is infinity. She did not like that answer one bit (and I can’t blame her). Her number sense comes almost completely from the number line (counting), and so she wanted to know where infinity was in the counting sequence. Makes sense, right? Some of the answers to her other questions were easier for her to digest (“what’s infinity plus infinity?”). In the end, though, she formulated an equation that made us both happy: Dad equals math.