then it automatically has `Eq`

! Witness:
```
instance (Group g, MonoidNull g) => Eq g where
x == y = null (x <> inv y)
```

See that this is a transport principle: we're able to transport the test
of equality at the origin/`mempty`

provided by `null`

to any point in the
group.
Olaf Klinke remarked:
A beautiful example of topological groups: Their topology is completely determined by the neighbourhoods of the identity element. If the identity element is isolated, the entire group is discrete.

I found this very interesting, because he's vieweing this from the
"topology of computation" lens, where the existence of `null`

means that
the identity element is isolated. Now since it is a topological group (group
operations are continuous since everything is computable!),
the isolatedness of the identity transports to all points, giving us a discrete
object where equality is decidable! Below is an illustration of how I imagine
the situation.
#### § References