static MultiMap mapLike mapMultiMapValueLists(O func, MultiMap mm) {
  MultiMap m = similarEmptyMultiMap(mm);
  for (O key : keys(mm))
    for (O value : mm.getActual(key))
      m.addAll(key, (Cl) callF(func, value));
  ret m;
}

static MultiMap mapMultiMapValueLists(MultiMap mm, O func) {
  ret mapMultiMapValueLists(func, mm);
}

static <A, B, C, D extends Cl<C>> MultiMap<A, C> mapMultiMapValueLists(IF1<B, D> func, MultiMap<A, B> mm) {
  ret mapMultiMapValueLists((O) func, mm);
}

Began life as a copy of #1020213