static <A, B> IterableIterator<B> navigableMultiSetMapValuesIterator_concurrent(final MultiSetMap<A, B> mm) {
  ret navigableMultiSetMapValuesIterator_concurrent(mm, mm.data);
}
  
static <A, B> IterableIterator<B> navigableMultiSetMapValuesIterator_concurrent(final MultiSetMap<A, B> mm, O mutex) {
  ret iteratorFromFunction(new F0<B>() {
    Iterator<Set<B>> it = concurrentlyIterateValues((NavigableMap) mm.data, mutex);
    Iterator<B> it2;
    
    public B get() {
      while (it2 == null || !it2.hasNext()) {
        if (!it.hasNext()) null;
        it2 = iterator(asList(it.next()));
      }
      ret it2.next();
    }
  });
}

Began life as a copy of #1013540