public Iterator<K> iterator() {
          return Iterators.unmodifiableIterator(delegate.keySet().iterator());
        }

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

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

    }
  }

  @Override
  public boolean containsKey(@CheckForNull Object key) {
    return asMap().get(key) != null;
  }

  @Override
  public Collection<V> removeAll(@CheckForNull Object key) {
    return MoreObjects.firstNonNull(asMap().remove(key), unmodifiableEmptyCollection());
  }

  Collection<V> unmodifiableEmptyCollection() {

      Set<Object> keys = cache.asMap().keySet();
      assertFalse(keys.remove(null));
      assertFalse(keys.remove(6));
      assertFalse(keys.remove(-6));
      assertFalse(keys.removeAll(asList(null, 0, 15, 1500)));
      assertFalse(keys.retainAll(asList(null, 0, 15, 1500)));
      checkEmpty(keys);
      checkEmpty(cache);
    }
  }

  public void testKeySet_remove() {

      Set<Object> keys = cache.asMap().keySet();
      assertFalse(keys.remove(null));
      assertFalse(keys.remove(6));
      assertFalse(keys.remove(-6));
      assertFalse(keys.removeAll(asList(null, 0, 15, 1500)));
      assertFalse(keys.retainAll(asList(null, 0, 15, 1500)));
      checkEmpty(keys);
      checkEmpty(cache);
    }
  }

  public void testKeySet_remove() {

      // invalidated and have undefined behavior after entrySet.removeAll(entriesToRemove),
      // for example entryToRemove.getValue() might be null.
      Entry<K, V> entryToRemoveCopy = mapEntry(entryToRemove.getKey(), entryToRemove.getValue());

      int initialSize = map.size();
      boolean didRemove = entrySet.removeAll(entriesToRemove);
      assertTrue(didRemove);

    } catch (UnsupportedOperationException expected) {
    }
    assertMultimapRemainsUnmodified(multimap, originalEntries);

    // Test #removeAll()
    try {
      multimap.removeAll(sampleKey);
      fail("removeAll succeeded on unmodifiable multimap");
    } catch (UnsupportedOperationException expected) {
    }
    assertMultimapRemainsUnmodified(multimap, originalEntries);

    }
  }

  @Override
  public boolean containsKey(@CheckForNull Object key) {
    return asMap().get(key) != null;
  }

  @Override
  public Collection<V> removeAll(@CheckForNull Object key) {
    return MoreObjects.firstNonNull(asMap().remove(key), unmodifiableEmptyCollection());
  }

  Collection<V> unmodifiableEmptyCollection() {

   * <p>This is equivalent to calling {@link #remove} on each of the ranges in {@code other} in
   * turn.
   *
   * @throws UnsupportedOperationException if this range set does not support the {@code removeAll}
   *     operation
   */
  void removeAll(RangeSet<C> other);

  /**
   * Removes all of the specified ranges from this range set (optional operation).
   *

      // invalidated and have undefined behavior after entrySet.removeAll(entriesToRemove),
      // for example entryToRemove.getValue() might be null.
      Entry<K, V> entryToRemoveCopy = mapEntry(entryToRemove.getKey(), entryToRemove.getValue());

      int initialSize = map.size();
      boolean didRemove = entrySet.removeAll(entriesToRemove);
      assertTrue(didRemove);

      return standardContainsAll(collection);
    }

    @Override
    public boolean remove(Object object) {
      return standardRemove(object);
    }

    @Override
    public boolean removeAll(Collection<?> collection) {
      return standardRemoveAll(collection);
    }

    @Override
    public boolean retainAll(Collection<?> collection) {
      return standardRetainAll(collection);
    }