static <A> A liftLast(L<A> l) {
  if (empty(l)) null;
  int i = l(l)-1;
  A a = l.get(i);
  l.remove(i);
  ret a;
}

static <A> L<A> liftLast(int n, L<A> l) {
  int i = l(l)-n;
  L<A> part = cloneSubList(l, i);
  removeSubList(l, i);
}