@Override
 protected void saveHelper(List<T> val, IStorage s) {
   GenericListStoreUnit<T> unit = new GenericListStoreUnit<T>(val, signature, io);
   s.put(factName, unit);
 }
 @Override
 @Nullable
 protected IStoreUnit<List<T>> loadHelper(IStorage s) throws IOException {
   return s.get(factName, new GenericListStoreUnit<T>(io));
 }