static <A> ItIt<A> roundRobinCombinedIterator(Iterator<A>... iterators) {
  class Robin implements IF0 {
    L<Iterator<A>> activeIterators = ll(iterators);
    int i;
    
    public O get() {
      while (nempty(activeIterators)) {
        Iterator<A> it = activeIterators.get(i);
        if (!it.hasNext()) { 
          activeIterators.remove(i);
          i = i % l(activeIterators);
        } else {
          i = (i+1) % l(activeIterators);
          ret it.next();
        }
      }
      ret endMarker();
    }
  }
  
  ret iff(new Robin);
}