{-
Returns `True` if there are an even number of `False` elements in the list and
returns `False` otherwise

Examples:

```
./even ([ False, True, False ] : List Bool) = True

./even ([ False, True ] : List Bool) = False

./even ([ False ] : List Bool) = False

./even ([] : List Bool) = True
```
-}
    let even
        : List Bool → Bool
        =   λ(xs : List Bool)
          → List/fold Bool xs Bool (λ(x : Bool) → λ(y : Bool) → x == y) True

in  even