code: @SuppressWarnings("unchecked")
    private T approximatelyAnswerPositionalQuery(final long pos) {
      assert 0 <= pos;
      assert pos < auxN_;
      final int index = QuantilesHelper.chunkContainingPos(auxCumWtsArr_, pos);
      return (T) this.auxSamplesArr_[index];
    }
docs: Assuming that there are n items in the true stream, this asks what
  item would appear in position 0 &le; pos &lt; n of a hypothetical sorted
  version of that stream.
  
  <p>Note that since that since the true stream is unavailable,
  we don't actually answer the question for that stream, but rather for
  a <i>different</i> stream of the same length, that could hypothetically
  be reconstructed from the weighted samples in our sketch.
  @param pos position
  @return approximate answer