{-
Returns `True` if the supplied function returns `True` for a present element and
`False` otherwise

Examples:

```
./any Natural Natural/even ([ +2 ] : Optional Natural) = True

./any Natural Natural/even ([] : Optional Natural) = False
```
-}
    let any
        : ∀(a : Type) → (a → Bool) → Optional a → Bool
        =   λ(a : Type)
          → λ(f : a → Bool)
          → λ(xs : Optional a)
          → Optional/fold a xs Bool f False

in  any