*
   * <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");

    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);

              }
            });
  }

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

   */
  public static <E extends @Nullable Object> SetView<E> union(
      Set<? extends E> set1, Set<? extends E> set2) {
    checkNotNull(set1, "set1");
    checkNotNull(set2, "set2");

    return new SetView<E>() {
      @Override
      public int size() {
        int size = set1.size();
        for (E e : set2) {
          if (!set1.contains(e)) {
            size++;
          }
        }
        return size;

                return wrap(delegate);
              }
            });
  }

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

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

              }
            });
  }

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

              }
            });
  }

  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();
  }

              }
            });
  }

  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();
  }

    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;

                return wrap(delegate);
              }
            });
  }

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