// 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();

import org.jspecify.annotations.Nullable;

/**
 * Skeletal implementation of {@link ImmutableSortedSet#descendingSet()}.
 *
 * @author Louis Wasserman
 */
@GwtIncompatible
final class DescendingImmutableSortedSet<E> extends ImmutableSortedSet<E> {
  private final ImmutableSortedSet<E> forward;

  DescendingImmutableSortedSet(ImmutableSortedSet<E> forward) {
    super(Ordering.from(forward.comparator()).reverse());

        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");
  }

import org.jspecify.annotations.Nullable;

/**
 * Skeletal implementation of {@link ImmutableSortedSet#descendingSet()}.
 *
 * @author Louis Wasserman
 */
@GwtIncompatible
final class DescendingImmutableSortedSet<E> extends ImmutableSortedSet<E> {
  private final ImmutableSortedSet<E> forward;

  DescendingImmutableSortedSet(ImmutableSortedSet<E> forward) {
    super(Ordering.from(forward.comparator()).reverse());

    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());

            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();

            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(

        }
      };
    }

    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(

    return (valueComparator == null)
        ? ImmutableSet.copyOf(values)
        : ImmutableSortedSet.copyOf(valueComparator, values);
  }

  private static <V> ImmutableSet<V> emptySet(@Nullable Comparator<? super V> valueComparator) {
    return (valueComparator == null)
        ? ImmutableSet.of()
        : ImmutableSortedSet.emptySet(valueComparator);
  }

  private static <V> ImmutableSet.Builder<V> valuesBuilder(