* returns an {@code ImmutableRangeSet}.
   *
   * @since 21.0
   */
  public ImmutableRangeSet<C> union(RangeSet<C> other) {
    return unionOf(Iterables.concat(asRanges(), other.asRanges()));
  }

  /**
   * Returns a new range set consisting of the intersection of this range set and {@code other}.
   *
   * <p>This is essentially the same as {@code