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

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

    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;
        };

    BiPredicate<ImmutableSortedSet<String>, ImmutableSortedSet<String>> equivalence =
        (set1, set2) ->
            set1.equals(set2)
                && set1.asList().equals(set2.asList())
                && set1.comparator().equals(set2.comparator());
    ImmutableSortedSet<String> expected =
        ImmutableSortedSet.orderedBy(String.CASE_INSENSITIVE_ORDER).add("a", "B", "c", "d").build();

   * @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() {}

   * @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() {}