static <A, B> Map<A, B> mapWithoutKey(Map<A, B> map, A key) {
  if (map == null || !map.containsKey(key)) ret map;
  Map m = cloneMap(map);
  m.remove(key);
  ret m;
}

static <A, B> Map<A, B> mapWithoutKey(A key, Map<A, B> map) {
  ret mapWithoutKey(map, key);
}