static <A, B, C extends Cl<B>> MultiMap<A, B> mapToMultiMap(Map<A, C> map) {
  if (map == null) null;
  MultiMap<A, B> mm = similarEmptyMultiMap(map);
  for (A key, Cl<B> values : map)
    mm.putAll(key, values);
  ret mm;
}

static <A, B, C> MultiMap<B, C> lambdaMapLike mapToMultiMap(IF1<A, Pair<B, C>> f, Iterable<A> l) {
  new MultiMap<B, C> mm;
  fOr (A o : l) {
    Pair<B, C> p = f.get(o);
    mm.put(p.a, p.b);
  }
  ret mm;
}

static <A, B, C> MultiMap<B, C> mapToMultiMap(Iterable<A> l, IF1<A, Pair<B, C>> f) {
  ret mapToMultiMap(f, l);
}