class Stamp implements Serializable {

    public Stamp event() {
        Event filled = Filler.fill(id, event);
        if (!filled.equals(event)) {
            return new Stamp(id, filled);
        }
        else {
            return new Stamp(id, Grower.grow(id, event));
        }
    }

    public  Stamp();
      Stamp(ID id, Event event);

}