public boolean retainAll(Collection<?> c) {
          return delegate.keySet().retainAll(c);
        }
      };
    }

    @Override
    public Collection<V> values() {
      return new ForwardingCollection<V>() {
        @Override
        protected Collection<V> delegate() {
          return delegate.values();
        }

        @Override
        public Iterator<V> iterator() {

        public boolean retainAll(Collection<?> c) {
          return delegate.keySet().retainAll(c);
        }
      };
    }

    @Override
    public Collection<V> values() {
      return new ForwardingCollection<V>() {
        @Override
        protected Collection<V> delegate() {
          return delegate.values();
        }

        @Override
        public Iterator<V> iterator() {

      }
    };
  }

  /** The implementation of {@link Multimaps#unmodifiableEntries}. */
  static class UnmodifiableEntries<K extends @Nullable Object, V extends @Nullable Object>
      extends ForwardingCollection<Entry<K, V>> {
    private final Collection<Entry<K, V>> entries;

    UnmodifiableEntries(Collection<Entry<K, V>> entries) {
      this.entries = entries;
    }

    @Override