Implement an Iterator of Iterators which traverses through an arbitrary number of iterators. IE, an iterator which iterates over three list iterators in the following way: L1 = a1, a2, a3 L2 = b1, b2, b3 L3 = c1, c2, c3 Then the iterator should process them in this order: a1, b1, c1, a2, b2, c2, a3, b3, c3