static <A> F0<A> f0_randomLL_differentEveryTime(final A... l) {
  if (l(l) < 2) fail("that makes no sense");
  
  ret new F0<A>() {
    int last = -1;
    
    public A get() {
      int idx;
      if (last == -1) idx = random(l(l));
      else {
        idx = random(l(l)-1);
        if (idx >= last) ++idx;
      }
      last = idx;
      ret get(l, idx);
    }
  };
}