" I feel empty when Root isn’t here,” I said. I hadn’t really been speaking to him, but the Professor murmured in reply, “So, you’re saying that there’s a zero in you?” “I suppose that’s what I mean,” I said, nodding weakly. “The person who discovered zero must have been remarkable, don’t you think?” “Hasn’t zero been around forever?” “How long is forever? "

― Yōko Ogawa , The Housekeeper and the Professor