}

  /**
   * Delegates to {@link Collection#contains}. Returns {@code false} if the {@code contains} method
   * throws a {@code ClassCastException} or {@code NullPointerException}.
   */
  static boolean safeContains(Collection<?> collection, @CheckForNull Object object) {
    checkNotNull(collection);
    try {
      return collection.contains(object);
    } catch (ClassCastException | NullPointerException e) {

  }

  /**
   * Delegates to {@link Collection#contains}. Returns {@code false} if the {@code contains} method
   * throws a {@code ClassCastException} or {@code NullPointerException}.
   */
  static boolean safeContains(Collection<?> collection, @CheckForNull Object object) {
    checkNotNull(collection);
    try {
      return collection.contains(object);
    } catch (ClassCastException | NullPointerException e) {

      @Override
      protected Set<E> delegate() {
        return delegate;
      }

      @Override
      public boolean contains(@CheckForNull Object object) {
        return object != null && Collections2.safeContains(delegate, object);
      }

      @Override
      public boolean containsAll(Collection<?> collection) {
        return standardContainsAll(collection);
      }

      @Override

      @Override
      protected Set<E> delegate() {
        return delegate;
      }

      @Override
      public boolean contains(@CheckForNull Object object) {
        return object != null && Collections2.safeContains(delegate, object);
      }

      @Override
      public boolean containsAll(Collection<?> collection) {
        return standardContainsAll(collection);
      }

      @Override

        if (obj instanceof Entry) {
          Entry<?, ?> entry = (Entry<?, ?>) obj;
          return entry.getKey() != null
              && entry.getValue() instanceof Map
              && Collections2.safeContains(backingMap.entrySet(), entry);
        }
        return false;
      }

      @Override
      public boolean remove(@CheckForNull Object obj) {
        if (obj instanceof Entry) {

      }

      // The following methods are included for performance.

      @Override
      public boolean contains(@CheckForNull Object o) {
        return Collections2.safeContains(submap.entrySet(), o);
      }

      @Override
      public boolean remove(@CheckForNull Object o) {
        if (!contains(o)) {
          return false;
        }

      }

      // The following methods are included for performance.

      @Override
      public boolean contains(@CheckForNull Object o) {
        return Collections2.safeContains(submap.entrySet(), o);
      }

      @Override
      public boolean remove(@CheckForNull Object o) {
        if (!contains(o)) {
          return false;
        }

      Iterable<? extends @Nullable Object> iterable, @CheckForNull Object element) {
    if (iterable instanceof Collection) {
      Collection<?> collection = (Collection<?>) iterable;
      return Collections2.safeContains(collection, element);
    }
    return Iterators.contains(iterable.iterator(), element);
  }

  /**
   * Removes, from an iterable, every element that belongs to the provided collection.
   *

      Iterable<? extends @Nullable Object> iterable, @CheckForNull Object element) {
    if (iterable instanceof Collection) {
      Collection<?> collection = (Collection<?>) iterable;
      return Collections2.safeContains(collection, element);
    }
    return Iterators.contains(iterable.iterator(), element);
  }

  /**
   * Removes, from an iterable, every element that belongs to the provided collection.
   *

    public boolean containsKey(@CheckForNull Object key) {
      return backingSet().contains(key);
    }

    @Override
    @CheckForNull
    public V get(@CheckForNull Object key) {
      if (Collections2.safeContains(backingSet(), key)) {
        @SuppressWarnings("unchecked") // unsafe, but Javadoc warns about it
        K k = (K) key;
        return function.apply(k);
      } else {
        return null;
      }
    }