public Set<Multiset.Entry<E>> entrySet() {
      Set<Multiset.Entry<E>> es = entrySet;
      return (es == null)
          // Safe because the returned set is made unmodifiable and Entry
          // itself is readonly
          ? entrySet = (Set) Collections.unmodifiableSet(delegate.entrySet())
          : es;
    }

    @Override
    public Iterator<E> iterator() {