sS lcStream_prediction(LCStreamingCompressor comp) {
  LineComp_PairIndex.Node tail = comp.chain.tail;
  if (tail == null) null;
  //print("tail", tail);
  OptimizedMultiSet<Int> partners = comp.popularRightPartners.get(tail.value);
  if (partners == null) null;
  //print(+partners);
  ret comp.itemToString(partners.getMostPopularEntry());
}