// TODO: work the other way around when set is small
static <A, B> Map<A, B> onlyKeys(Map<A, B> map, Cl<A> keys) {
  Set<A> keySet = asSet(keys);
  ret filterKeys(map, a -> contains(keySet, a));
}

static <A, B> Map<A, B> onlyKeys(Map<A, B> map, A... keys) {
  ret onlyKeys(map, litset(keys));
}