import java.util.ArrayList;
import java.util.List;


public class Leaf implements Node{
  private static Leaf empty = new Leaf();
  private Leaf(){
  }
  public static Leaf getLeafInstance(){
    return empty;
  }
  public Node add(int key){
    return new InternalNode(key,getLeafInstance(),getLeafInstance());
  }
  @Override public String toString(){
    return "";
  }
  public Pair<Node> cut(int key){
    return new Pair<Node>(getLeafInstance(),getLeafInstance());
 }
  public List<Integer> toList(){
    return new ArrayList<Integer>();
  }
}