code: ReservoirItemsSketch<T> downsampledCopy(final int maxK) {
      final ReservoirItemsSketch<T> ris = new ReservoirItemsSketch<>(maxK, rf_);
      for (final T item : getSamples()) {
        // Pretending old implicit weights are all 1. Not true in general, but they're all
        // equal so update should work properly as long as we update itemsSeen_ at the end.
        ris.update(item);
      }
  
      // need to adjust number seen to get correct new implicit weights
      if (ris.getN() < itemsSeen_) {
        ris.forceIncrementItemsSeen(itemsSeen_ - ris.getN());
      }
  
      return ris;
    }
docs: temporary violation of maxK, we're avoiding violating it at all.