Type Alias _N<T, $O>

_N<T, $O>: [T] extends [number & infer U]
    ? U extends number
        ? $ResolveBranch<T, $O, [$Else]>
        : $ResolveBranch<T, $O, [$Then]>
    : $ResolveBranch<T, $O, [$Then]>