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

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

    /**
     * Returns the default equivalence strategy used to compare and hash keys or values referenced

  /**
   * Returns the empty iterator.
   *
   * <p>The {@link Iterable} equivalent of this method is {@link ImmutableSet#of()}.
   */
  static <T extends @Nullable Object> UnmodifiableIterator<T> emptyIterator() {
    return emptyListIterator();
  }

  /**
   * Returns the empty iterator.
   *
   * <p>The {@link Iterable} equivalent of this method is {@link ImmutableSet#of()}.
   */

    assertFalse(actual.contains(list(3, 1)));
  }

  public void testCartesianProduct_equals() {
    Set<List<Integer>> cartesian = Sets.cartesianProduct(set(1, 2), set(3, 4));
    ImmutableSet<List<Integer>> equivalent =
        ImmutableSet.of(ImmutableList.of(1, 3), ImmutableList.of(1, 4), list(2, 3), list(2, 4));
    ImmutableSet<List<Integer>> different1 =

   */
  public CharMatcher or(CharMatcher other) {
    return new Or(this, other);
  }

  /**
   * Returns a {@code char} matcher functionally equivalent to this one, but which may be faster to
   * query than the original; your mileage may vary. Precomputation takes time and is likely to be
   * worthwhile only if the precomputed matcher is queried many thousands of times.
   *

   */
  public CharMatcher or(CharMatcher other) {
    return new Or(this, other);
  }

  /**
   * Returns a {@code char} matcher functionally equivalent to this one, but which may be faster to
   * query than the original; your mileage may vary. Precomputation takes time and is likely to be
   * worthwhile only if the precomputed matcher is queried many thousands of times.
   *

    private transient @Nullable Object[] keys;
    private transient @Nullable Object[] values;
    private final Comparator<? super K> comparator;

    /**
     * Creates a new builder. The returned builder is equivalent to the builder generated by {@link
     * ImmutableSortedMap#orderedBy}.
     */
    public Builder(Comparator<? super K> comparator) {
      this(comparator, ImmutableCollection.Builder.DEFAULT_INITIAL_CAPACITY);

   * @since 2.0
   */
  public static class Builder<K, V> extends ImmutableMap.Builder<K, V> {
    private final Comparator<? super K> comparator;

    /**
     * Creates a new builder. The returned builder is equivalent to the builder generated by {@link
     * ImmutableSortedMap#orderedBy}.
     */
    public Builder(Comparator<? super K> comparator) {
      this.comparator = checkNotNull(comparator);
    }

    /**

    }

    /**
     * Copies the current contents of this set view into an existing set. This method has equivalent
     * behavior to {@code set.addAll(this)}, assuming that all the sets involved are based on the
     * same notion of equivalence.
     *
     * @return a reference to {@code set}, for convenience
     */
    // Note: S should logically extend Set<? super E> but can't due to either

  /**
   * Returns the empty iterator.
   *
   * <p>The {@link Iterable} equivalent of this method is {@link ImmutableSet#of()}.
   */
  static <T extends @Nullable Object> UnmodifiableIterator<T> emptyIterator() {
    return emptyListIterator();
  }

  /**
   * Returns the empty iterator.
   *
   * <p>The {@link Iterable} equivalent of this method is {@link ImmutableSet#of()}.
   */

    if (future instanceof Trusted) {
      // Break encapsulation for TrustedFuture instances since we know that subclasses cannot
      // override .get() (since it is final) and therefore this is equivalent to calling .get()
      // and unpacking the exceptions like we do below (just much faster because it is a single
      // field read instead of a read, several branches and possibly creating exceptions).