} 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<?>>

      }

      ImmutableRangeSet<Integer> built = builder.build();
      assertEquals(mutable, built);
      assertEquals(ImmutableRangeSet.copyOf(mutable), built);
      assertEquals(mutable.complement(), built.complement());

      for (int i = 0; i <= 11; i++) {
        assertEquals(mutable.contains(i), built.contains(i));
      }

      SerializableTester.reserializeAndAssert(built);

    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