product

{-
Multiply all the numbers in a `List`

Examples:

```
./product ([ +2, +3, +5 ] : List Natural) = +30

./product ([] : List Natural) = +1
```
-}
    let product
        : List Natural → Natural
        =   λ(xs : List Natural)
          → List/fold
            Natural
            xs
            Natural
            (λ(l : Natural) → λ(r : Natural) → l * r)
            +1

in  product