static <A, B> ItIt<Pair<A, B>> multiMapPairIterator_transformValueList(MultiMap<A, B> mm, IF1<L<B>> f) {
  ret nestedIterator(iterator(keys(mm.data)), key ->
    (ItIt<Pair<A,B>>) mapI(iterator(f.get(mm.data.get(key))), val -> pair(key, val)));
}