static MultiMap litmultimap(O... x) {
  new HashMap map;
  litmultimap_impl(map, x);
  ret map;
}

static void litmultimap_impl(MultiMap map, O... x) {
  for (int i = 0; i < x.length-1; i += 2)
    if (x[i+1] != null)
      map.put(x[i], (L) x[i+1]);
}