# Problem

Why does the doc test for `sub` under `impl<T> Sub for Point2<T>` work, but my
attempt to implement `area` under `impl<T> Bounds2<T>` fails to compile with:

```
error[E0369]: binary operation `-` cannot be applied to type `Point2<T>`
  --> src/lib.rs:87:28
   |
87 |         let d = self.p_max - self.p_min;
   |                 ---------- ^ ---------- Point2<T>
   |                 |
   |                 Point2<T>
   |
   = note: an implementation of `std::ops::Sub` might be missing for `Point2<T>`
```