*
   * <p>Results are undefined if {@code set1} and {@code set2} are sets based on different
   * equivalence relations, for example if {@code set1} is a {@link HashSet} and {@code set2} is a
   * {@link TreeSet} or the {@link Map#keySet} of an {@code IdentityHashMap}.
   */
  public static <E extends @Nullable Object> SetView<E> difference(Set<E> set1, Set<?> set2) {
    checkNotNull(set1, "set1");
    checkNotNull(set2, "set2");

        .addEqualityGroup(set2, wrap(set2))
        .testEquals();
  }

  private static <T> Set<T> wrap(Set<T> delegate) {
    return new ForwardingSet<T>() {
      @Override
      protected Set<T> delegate() {
        return delegate;
      }
    };
  }

              }
            });
  }

  public void testEquals() {
    SortedMultiset<String> set1 = ImmutableSortedMultiset.of("one");
    SortedMultiset<String> set2 = ImmutableSortedMultiset.of("two");
    new EqualsTester()
        .addEqualityGroup(set1, wrap(set1), wrap(set1))
        .addEqualityGroup(set2, wrap(set2))
        .testEquals();
  }

  private static <T> SortedMultiset<T> wrap(SortedMultiset<T> delegate) {

    Set<Integer> set2 = newHashSet(2, 3);
    Set<Integer> difference = difference(set1, set2);
    assertThat(difference).containsExactly(1);
    set1.add(0);
    assertThat(difference).containsExactly(0, 1);
    set2.remove(2);
    assertThat(difference).containsExactly(0, 1, 2);
  }

  public void testSymmetricDifference_isView() {
    Set<Integer> set1 = newHashSet(1, 2);
    Set<Integer> set2 = newHashSet(2, 3);

        .addEqualityGroup(set2, wrap(set2))
        .testEquals();
  }

  private static <T> Set<T> wrap(Set<T> delegate) {
    return new ForwardingSet<T>() {
      @Override
      protected Set<T> delegate() {
        return delegate;
      }
    };
  }

              }
            });
  }

  public void testEquals() {
    SortedMultiset<String> set1 = ImmutableSortedMultiset.of("one");
    SortedMultiset<String> set2 = ImmutableSortedMultiset.of("two");
    new EqualsTester()
        .addEqualityGroup(set1, wrap(set1), wrap(set1))
        .addEqualityGroup(set2, wrap(set2))
        .testEquals();
  }

  private static <T> SortedMultiset<T> wrap(SortedMultiset<T> delegate) {

    BiPredicate<ImmutableSet<TypeWithDuplicates>, ImmutableSet<TypeWithDuplicates>> equivalence =
        (set1, set2) -> {
          if (!set1.equals(set2)) {
            return false;
          }
          for (int i = 0; i < set1.size(); i++) {
            if (!set1.asList().get(i).fullEquals(set2.asList().get(i))) {
              return false;
            }
          }
          return true;
        };

    assertTrue(set.containsAll(Sets.newTreeSet(asList("a", "b", "f"))));
    assertFalse(set.containsAll(Sets.newTreeSet(asList("d"))));
    assertFalse(set.containsAll(Sets.newTreeSet(asList("z"))));
    assertFalse(set.containsAll(Sets.newTreeSet(asList("b", "d"))));
    assertFalse(set.containsAll(Sets.newTreeSet(asList("f", "d", "a"))));
  }

  }

  /**
   * Construct a new {@link java.util.Set} that is the intersection of the given sets.
   *
   * @deprecated Use {@link com.google.common.collect.Sets#intersection(Set, Set)} instead.
   */
  @Deprecated
  public static <T> Set<T> intersection(Set<? extends T> set1, Set<? extends T> set2) {
    Set<T> result = copyToSet(set1);
    result.retainAll(set2);
    return result;
  }

  private FeatureUtil() {}

  }

  /**
   * Construct a new {@link java.util.Set} that is the intersection of the given sets.
   *
   * @deprecated Use {@link com.google.common.collect.Sets#intersection(Set, Set)} instead.
   */
  @Deprecated
  public static <T> Set<T> intersection(Set<? extends T> set1, Set<? extends T> set2) {
    Set<T> result = copyToSet(set1);
    result.retainAll(set2);
    return result;
  }

  private FeatureUtil() {}