return multimap.keySet().size();
    }

    @Override
    protected Set<Entry<K, Collection<V>>> createEntrySet() {
      return new EntrySet();
    }

    void removeValuesForKey(@CheckForNull Object key) {
      multimap.keySet().remove(key);
    }

    @WeakOuter
    class EntrySet extends Maps.EntrySet<K, Collection<V>> {
      @Override