static LS longerThan(Iterable<S> l, int x) {
  ret filter(l, s -> l(s) > x);
}

static LS longerThan(int x, Iterable<S> l) {
  ret longerThan(l, x);
}

static <A, B> bool longerThan(Cl<A> a, Cl<B> b) {
  ret l(a) > l(b);
}