return ImmutableSortedSet.copyOf(elements);
    }
  }

  public static class ImmutableSortedSetHeadsetGenerator extends TestStringSortedSetGenerator {
    @Override
    protected SortedSet<String> create(String[] elements) {
      List<String> list = Lists.newArrayList(elements);
      list.add("zzz");
      return ImmutableSortedSet.copyOf(list).headSet("zzy");
    }
  }

    // Note that a Collector should generally enforce consistent comparator between builders
    ImmutableSortedSet.Builder<String> zis =
        ImmutableSortedSet.<String>naturalOrder().add("c", "b", "c");
    ImmutableSortedSet.Builder<String> zat =
        ImmutableSortedSet.<String>naturalOrder().add("a", "b", "d", "c");
    ImmutableSortedSet<String> sortedSet = zis.combine(zat).build();

            ContiguousSet.create(Range.open(0, 4), NOT_EQUAL_TO_INTEGERS),
            ImmutableSortedSet.of(1, 2, 3))
        .addEqualityGroup(
            ContiguousSet.create(Range.closedOpen(1, 1), integers()),
            ContiguousSet.closedOpen(1, 1),
            ContiguousSet.closedOpen(Integer.MIN_VALUE, Integer.MIN_VALUE),
            ImmutableSortedSet.of(),
            ImmutableSet.of())
        .testEquals();

        Equivalence.equals()
            .onResultOf(ImmutableSortedSet<String>::comparator)
            .and(Equivalence.equals().onResultOf(ImmutableSortedSet::asList))
            .and(Equivalence.equals());
    CollectorTester.of(collector, equivalence)
        .expectCollects(
            ImmutableSortedSet.of("a", "b", "c", "d"), "a", "b", "a", "c", "b", "b", "d");
  }

          .put(ImmutableList.class, ImmutableList.of())
          .put(Set.class, ImmutableSet.of())
          .put(ImmutableSet.class, ImmutableSet.of())
          .put(SortedSet.class, ImmutableSortedSet.of())
          .put(ImmutableSortedSet.class, ImmutableSortedSet.of())
          .put(NavigableSet.class, Sets.unmodifiableNavigableSet(Sets.newTreeSet()))
          .put(Map.class, ImmutableMap.of())
          .put(ImmutableMap.class, ImmutableMap.of())

  }

  static <E> Collector<E, ?, ImmutableSortedSet<E>> toImmutableSortedSet(
      Comparator<? super E> comparator) {
    checkNotNull(comparator);
    return Collector.of(
        () -> new ImmutableSortedSet.Builder<E>(comparator),
        ImmutableSortedSet.Builder::add,
        ImmutableSortedSet.Builder::combine,
        ImmutableSortedSet.Builder::build);
  }

    assertTrue(multimap.get("a") instanceof ImmutableSortedSet);
    assertEquals(
        Collections.reverseOrder(), ((ImmutableSortedSet<Integer>) multimap.get("a")).comparator());
    assertTrue(multimap.get("x") instanceof ImmutableSortedSet);
    assertEquals(
        Collections.reverseOrder(), ((ImmutableSortedSet<Integer>) multimap.get("x")).comparator());

    } else {
      return ~index;
    }
  }

  @Override
  ImmutableSortedSet<E> subSetImpl(
      E fromElement, boolean fromInclusive, E toElement, boolean toInclusive) {
    return tailSetImpl(fromElement, fromInclusive).headSetImpl(toElement, toInclusive);
  }

  @Override
  ImmutableSortedSet<E> tailSetImpl(E fromElement, boolean inclusive) {

            ContiguousSet.create(Range.open(0, 4), NOT_EQUAL_TO_INTEGERS),
            ImmutableSortedSet.of(1, 2, 3))
        .addEqualityGroup(
            ContiguousSet.create(Range.closedOpen(1, 1), integers()),
            ContiguousSet.closedOpen(1, 1),
            ContiguousSet.closedOpen(Integer.MIN_VALUE, Integer.MIN_VALUE),
            ImmutableSortedSet.of(),
            ImmutableSet.of())
        .testEquals();

        }
      };
    }

    ImmutableSortedSet<C> subSet(Range<C> range) {
      return subRangeSet(range).asSet(domain);
    }

    @Override
    ImmutableSortedSet<C> headSetImpl(C toElement, boolean inclusive) {
      return subSet(Range.upTo(toElement, BoundType.forBoolean(inclusive)));
    }

    @Override
    ImmutableSortedSet<C> subSetImpl(