/// Array can contain same typed values.

// The elements infered as Array<Option<Vec<Nat>>>.
let x = [None, Some([1]), None, Some([]), None];

// Unknown part is typed with Any.
// This is `Array<Option<Array<Any>>>
let x = [None, Some([]), None, Some([]), None];

// Of course, you can annotate explicitly.
let x: Array<Option<Array<Nat>>> = [None, Some([])];

x