### What it does
Lints for suspicious operations in impls of arithmetic operators, e.g.
subtracting elements in an Add impl.

### Why is this bad?
This is probably a typo or copy-and-paste error and not intended.

### Example
```
impl Add for Foo {
    type Output = Foo;

    fn add(self, other: Foo) -> Foo {
        Foo(self.0 - other.0)
    }
}
```