static <A, B> Set<B> msmGetAllAsSet(MultiSetMap<A, B> mm, A... keys) {
  new Set<B> l;
  for (A key : keys)
    l.addAll(mm.get(key));
  ret l;
}

static <A, B> Set<B> msmGetAllAsSet(MultiSetMap<A, B> mm, Iterable<A> keys) {
  new Set<B> l;
  fOr (A key : keys)
    l.addAll(mm.get(key));
  ret l;
}