Main {{
  public static void p(String s){ System.out.print(s); }
  public static void main(String args[]) throws Exception {
    Start start = Start.parse(System.in); 
    // some sample functionality
    p(start.display() + "\n");
    p(start.print() + "\n");
    p(start.toStr() + "\n");
    System.out.println(start.equals(start));
    p(start.magic().display() + "\n");
    p(start.bottomUp() + "\n");
  }
}}

Start {{
  // magically replace apples by oranges and vice versa
  // and keep the rest of the structure the same
  public Start magic() {
    return new Traversal(new Bc(){
      Orange combine(Apple a){return new Orange();}
      Apple  combine(Orange o){return new Apple();}
    }).<Start> traverse(this);
  }
}}
Start {{
  public int bottomUp() {
    return new Traversal(new ID() {
      // add structure details gradually    
      int combine(Apple a){return 4;}

      // int combine(Pencil p){return 10;}
      int combine(Item p){return 10;}
      // bottomUp jumps from 20 to 73

      int combine(Empty e){return 0;}
      int combine(Cons o, int n1, int n2){return n1+n2;}
      // int combine(Object o, int n1){return n1;}
      int combine(Start o, int n1){return n1;}
      int combine(Basket o, int n1){return n1;}
      // interplay between structure-shyness and safety

      int combine(Fruit a){return 5;}
    
    }).<Integer> traverse(this);
  }
}}