* #weakKeys} is specified, and {@link Equivalence#equals()} otherwise. The only place this is
   * used is in {@link Interners.WeakInterner}.
   */
  @CanIgnoreReturnValue
  @GwtIncompatible // To be supported
  MapMaker keyEquivalence(Equivalence<Object> equivalence) {
    checkState(keyEquivalence == null, "key equivalence was already set to %s", keyEquivalence);

  private final Equivalence<T> resultEquivalence;

  FunctionalEquivalence(
      Function<? super F, ? extends @Nullable T> function, Equivalence<T> resultEquivalence) {
    this.function = checkNotNull(function);
    this.resultEquivalence = checkNotNull(resultEquivalence);
  }

  @Override
  protected boolean doEquivalent(F a, F b) {
    return resultEquivalence.equivalent(function.apply(a), function.apply(b));
  }

   * #weakKeys} is specified, and {@link Equivalence#equals()} otherwise. The only place this is
   * used is in {@link Interners.WeakInterner}.
   */
  @CanIgnoreReturnValue
  @GwtIncompatible // To be supported
  MapMaker keyEquivalence(Equivalence<Object> equivalence) {
    checkState(keyEquivalence == null, "key equivalence was already set to %s", keyEquivalence);

import java.util.Iterator;
import org.jspecify.annotations.Nullable;

@GwtCompatible
final class PairwiseEquivalence<E, T extends @Nullable E> extends Equivalence<Iterable<T>>
    implements Serializable {
  final Equivalence<E> elementEquivalence;

  PairwiseEquivalence(Equivalence<E> elementEquivalence) {
    this.elementEquivalence = Preconditions.checkNotNull(elementEquivalence);
  }

  @Override

import java.util.Iterator;
import org.jspecify.annotations.Nullable;

@GwtCompatible
final class PairwiseEquivalence<E, T extends @Nullable E> extends Equivalence<Iterable<T>>
    implements Serializable {
  final Equivalence<E> elementEquivalence;

  PairwiseEquivalence(Equivalence<E> elementEquivalence) {
    this.elementEquivalence = Preconditions.checkNotNull(elementEquivalence);
  }

  @Override

    BiPredicate<ImmutableSortedMap<String, Integer>, ImmutableSortedMap<String, Integer>>
        equivalence =
            Equivalence.equals()
                .onResultOf(ImmutableSortedMap<String, Integer>::comparator)
                .and(Equivalence.equals().onResultOf(map -> map.entrySet().asList()))
                .and(Equivalence.equals());
    ImmutableSortedMap<String, Integer> expected =

  }

  public void testToImmutableSet() {
    Collector<String, ?, ImmutableSet<String>> collector = toImmutableSet();
    Equivalence<ImmutableSet<String>> equivalence =
        Equivalence.equals().onResultOf(ImmutableSet::asList);
    CollectorTester.of(collector, equivalence)
        .expectCollects(ImmutableSet.of("a", "b", "c", "d"), "a", "b", "a", "c", "b", "b", "d");
  }

  }

  public void testToImmutableMultiset() {
    BiPredicate<ImmutableMultiset<String>, ImmutableMultiset<String>> equivalence =
        (ms1, ms2) -> ms1.equals(ms2) && ms1.entrySet().asList().equals(ms2.entrySet().asList());
    CollectorTester.of(ImmutableMultiset.<String>toImmutableMultiset(), equivalence)
        .expectCollects(ImmutableMultiset.of())
        .expectCollects(

        .addEquivalenceGroup("a")
        .test();
  }

  public void testEquals() {
    new EqualsTester()
        .addEqualityGroup(Equivalence.equals(), Equivalence.equals())
        .addEqualityGroup(Equivalence.identity(), Equivalence.identity())
        .testEquals();
  }

  @J2ktIncompatible
  @GwtIncompatible // NullPointerTester
  public void testNulls() throws NoSuchMethodException {

     */

    STRONG {
      @Override
      Equivalence<Object> defaultEquivalence() {
        return Equivalence.equals();
      }
    },

    SOFT {
      @Override
      Equivalence<Object> defaultEquivalence() {
        return Equivalence.identity();
      }
    },

    WEAK {
      @Override
      Equivalence<Object> defaultEquivalence() {
        return Equivalence.identity();