static <A, B> LL<B> mapTwoLevelsDown(F1<A, B> f, LL<A> l) {
  new LL<B> out;
  for (L<A> x : l)
    out.add(map(f, x));
  ret out;
}

static LL mapLike levelTwoMap(O f, LL l) {
  new LL out;
  for (L x : l)
    out.add(map(f, x));
  ret out;
}