class AncestorChildExpansionIterator implements SortedKeyValueIterator<Key,Value> {

    @Override
    public void next() throws IOException {
        if (!seeked) {
            throw new IllegalStateException("cannot next(), iterator has not been seeked");
        }
        
        if (initialized && topKey == null) {
            throw new NoSuchElementException("cannot next(), iterator is empty");
        }
        
        nextChild();
    }

    public  AncestorChildExpansionIterator(SortedKeyValueIterator<Key,Value> iterator, List<String> children, Equality equality);

}