} catch (UnsupportedOperationException expected) {
    }
    assertCollectionsAreEquivalent(copy, collection);

    try {
      collection.retainAll(siblingCollection);
      fail("retainAll succeeded on unmodifiable collection");
    } catch (UnsupportedOperationException expected) {
    }
    assertCollectionsAreEquivalent(copy, collection);
  }

  /**

   * Multiset)}.
   *
   * <p>This method refines {@link Collection#retainAll} to further specify that it <b>may not</b>
   * throw an exception in response to any of {@code elements} being null or of the wrong type.
   *
   * @see Multisets#retainOccurrences(Multiset, Multiset)
   */
  @CanIgnoreReturnValue
  @Override
  boolean retainAll(Collection<?> c);

          }
        }
        return map().keySet().removeAll(toRemove);
      }
    }

    @Override
    public boolean retainAll(Collection<?> c) {
      try {
        return super.retainAll(checkNotNull(c));
      } catch (UnsupportedOperationException e) {
        Set<K> toRetain = new HashSet<>();
        for (Entry<K, V> entry : map().entrySet()) {

   * Multiset)}.
   *
   * <p>This method refines {@link Collection#retainAll} to further specify that it <b>may not</b>
   * throw an exception in response to any of {@code elements} being null or of the wrong type.
   *
   * @see Multisets#retainOccurrences(Multiset, Multiset)
   */
  @CanIgnoreReturnValue
  @Override
  boolean retainAll(Collection<?> c);

  /**
   * {@inheritDoc}
   *

    } catch (UnsupportedOperationException expected) {
    }
    assertCollectionsAreEquivalent(copy, collection);

    try {
      collection.retainAll(siblingCollection);
      fail("retainAll succeeded on unmodifiable collection");
    } catch (UnsupportedOperationException expected) {
    }
    assertCollectionsAreEquivalent(copy, collection);
  }

  /**

          }
        }
        return map().keySet().removeAll(toRemove);
      }
    }

    @Override
    public boolean retainAll(Collection<?> c) {
      try {
        return super.retainAll(checkNotNull(c));
      } catch (UnsupportedOperationException e) {
        Set<K> toRetain = new HashSet<>();
        for (Entry<K, V> entry : map().entrySet()) {

        }

        public boolean removeAll(final Collection<?> c) {
            return parent.removeAll(c);
        }

        public boolean retainAll(final Collection<?> c) {
            return parent.retainAll(c);
        }

        public void clear() {
            parent.clear();
        }

        public boolean equals(final Object o) {
            return parent.equals(o);

  public static <E extends @Nullable Object> Collection<E> filter(
      Collection<E> unfiltered, Predicate<? super E> predicate) {
    if (unfiltered instanceof FilteredCollection) {
      // Support clear(), removeAll(), and retainAll() when filtering a filtered
      // collection.
      return ((FilteredCollection<E>) unfiltered).createCombined(predicate);
    }

    return new FilteredCollection<>(checkNotNull(unfiltered), checkNotNull(predicate));

    @Override
    public boolean removeAll(Collection<?> c) {
      return removeAllImpl(this, c);
    }

    @Override
    public boolean retainAll(Collection<?> c) {
      return super.retainAll(checkNotNull(c)); // GWT compatibility
    }
  }

  /**
   * Returns an immutable set instance containing the given enum elements. Internally, the returned

      synchronized (mutex) {
        return delegate().removeAll(c);
      }
    }

    @Override
    public boolean retainAll(Collection<?> c) {
      synchronized (mutex) {
        return delegate().retainAll(c);
      }
    }

    @Override
    public int size() {
      synchronized (mutex) {
        return delegate().size();
      }
    }