I take the stairs instead of the elevator most nights, four flights, because I don't like standing in a box with a stranger this late and telling myself that's the whole reason.
On the third floor there's a mat outside 4C, crooked the same exact way for two weeks now, one corner folded under like nobody's touched it. The porch light under her door comes on every night around two, though. Someone's home. Or something is turning the light on for her.
I started taking a photo of the mat on my way up. Not to show anyone. Just so there'd be proof, later, that I checked. I have forty photos of the same crooked mat now, one folder, dated.
Tonight I stood there long enough to notice what I was actually doing, which isn't checking on her. Checking on her would mean knocking, and knocking would mean I'd have to do something with whatever answered. The photo lets me leave a record without leaving a mark.
I climbed the last flight and didn't look back at the light under her door. Tomorrow I'll take another picture. It'll look exactly like proof.