```
enumerate(iter)
```

is an iterator that yields (i, x) where i is a counter

starting at 1, and x is the i-th value from the given iterator.

How to define

```
enumerate(iter, start=0)
```

an iterator that yields (i+start, x) where i is a counter

starting at 1, and x is the i-th value from the given iterator?

More generally, there is Base.Iterators.countfrom(start=1, step=1)

which is an iterator starting at start and incrementing by step.

How to define

```
enumerate(iter, start=0, step=1)
```

which is an iterator that yields (i*step+start, x) where i

is a counter starting at 1, and x is the i-th value from the

given iterator?