iterator = topMetaIterator.next();

        if (iterator instanceof ConcatenatedIterator) {
          // Instead of taking linear time in the number of nested concatenations, unpack
          // them into the queue
          @SuppressWarnings("unchecked")
          ConcatenatedIterator<T> topConcat = (ConcatenatedIterator<T>) iterator;
          iterator = topConcat.iterator;