splitAt method
Splits into two after first n elements.
1, 2, 3.splitAt(1) = [1, 2, 3].
If n <= 0, returns [], this.
If n >= this.length, returns this, [].
Implementation
Set<Set<E>> splitAt(int n) {
return h.splitAtIterable(index: n, original: this).toNestedSet();
}