class Cell<A> {
  public A value;
  public Cell (A v) { value = v; }
  public static <B> Cell<B> allocate (B x) {
    return new Cell<B>(x);
  }
}

class Pair<A,B> {
  public A fst;
  public B snd;
  public Pair (A x, B y) { fst = x; snd = y; }
  public static <C> Pair<C,C> duplicate (C x) {
    return new Pair<C,C>(x,x);
  }
}

class Loophole {
  public static String loophole (Byte y) {
    Pair<Cell<String>,Cell<Byte>> p =
       Pair.duplicate(Cell.allocate(null)); // compile-time error
    p.snd.value = y; return p.fst.value;
  }
  public static String permitted (String x) {
    Pair<Cell<String>,Cell<String>> p =
       Pair.duplicate(Cell.allocate((String)null));
    p.fst.value = x; return p.snd.value;
  }
}