} else {
      rangesByLowerBound.put(range.lowerBound, range);
    }
  }

  @LazyInit private transient @Nullable RangeSet<C> complement;

  @Override
  public RangeSet<C> complement() {
    RangeSet<C> result = complement;
    return (result == null) ? complement = new Complement() : result;
  }

  @VisibleForTesting
  static final class RangesByUpperBound<C extends Comparable<?>>

    this(ranges, /* complement= */ null);
  }

  private ImmutableRangeSet(
      ImmutableList<Range<C>> ranges, @Nullable ImmutableRangeSet<C> complement) {
    this.ranges = ranges;
    this.complement = complement;
  }

  private final transient ImmutableList<Range<C>> ranges;
  private final transient @Nullable ImmutableRangeSet<C> complement;

  @Override

   * element, in order to determine the element type. If the collection could be empty, use {@link
   * #complementOf(Collection, Class)} instead of this method.
   *
   * @param collection the collection whose complement should be stored in the enum set
   * @return a new, modifiable {@code EnumSet} containing all values of the enum that aren't present
   *     in the given collection