Type alias FlatArray<Arr, Depth>
FlatArray<Arr, Depth>: { done: Arr; recur: Arr extends ReadonlyArray<infer InnerArr> ? FlatArray<InnerArr, [-1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20][Depth]> : Arr; }[Depth extends -1 ? "done" : "recur"]