Bubbler-4

#### Input range problem I think it's important to decide the structure of the underlying graph. Will it have one or more cycles? Will it have multiple connected components? Should...

A potential problem with this is that, if a `#[repr(u8)]` enum happens to have exactly 256 variants, the value of `COUNT` does not fit in `u8`.

I also got this lint today by typing `if r < n - r` and was puzzled as to how it could be an overflow check at all. `r <...