* builder.
     *
     * @throws IllegalArgumentException if any two ranges inserted into this builder overlap
     */
    public ImmutableRangeMap<K, V> build() {
      Collections.sort(entries, Range.<K>rangeLexOrdering().onKeys());
      ImmutableList.Builder<Range<K>> rangesBuilder = new ImmutableList.Builder<>(entries.size());
      ImmutableList.Builder<V> valuesBuilder = new ImmutableList.Builder<>(entries.size());

     * builder.
     *
     * @throws IllegalArgumentException if any two ranges inserted into this builder overlap
     */
    public ImmutableRangeMap<K, V> build() {
      Collections.sort(entries, Range.<K>rangeLexOrdering().onKeys());
      ImmutableList.Builder<Range<K>> rangesBuilder = new ImmutableList.Builder<>(entries.size());
      ImmutableList.Builder<V> valuesBuilder = new ImmutableList.Builder<>(entries.size());

    }
    return new RegularImmutableSortedSet<>(ranges, Range.<C>rangeLexOrdering());
  }

  @Override
  public ImmutableSet<Range<C>> asDescendingSetOfRanges() {
    if (ranges.isEmpty()) {
      return ImmutableSet.of();
    }
    return new RegularImmutableSortedSet<>(ranges.reverse(), Range.<C>rangeLexOrdering().reverse());
  }