Sitting perfectly still on the swings with the faraway traffic lights flashing weakly in the dark, Evelyn tells me that the two parts of the graph f(x)=1/x are separated by two asymptotes: one horizontal—with the slope approaching zero in that direction—and one vertical. I kick some mulch on the upswing and ask her what about the vertical. Her white rounded shoes make a heart as she brings her ankles together, and she says the slope approaches a denominator of zero. That’s so stupid, I said. You can’t divide by zero. At this point the air smelled like iron and sweat, or I did, anyways. I don’t know about Evelyn. I don’t think I ever thought Evelyn smelled like anything. But when the arc of my swing slowed until I decided to skid to a stop, there’s something smudged on the edge of Evelyn’s mouth, something she wipes away before looking at me for the first time that evening. For some reason I found that weirder than 1/x. That’s why I used the word approaches, Clara, she said—then added, a function can go anywhere if you’re okay with it never ending up where it wants to.