code: void merge(final long key, final double[] values) {
      setNotEmpty();
      if (key < theta_) {
        final int index = findOrInsertKey(key);
        if (index < 0) {
          incrementCount();
          setValues(~index, values);
        } else {
          updateValues(index, values);
        }
        rebuildIfNeeded();
      }
    }
docs: not sufficient by itself without keeping track of theta of another sketch