import java.util.*;
import java.lang.*;
 
class BinaryTree<E extends Comparable<E>> implements Iterable<E> {   
    public void add(E toInsert) {
        // ...
    }
 
    public Iterator<E> iterator() {
        return null;
    }
}
 
class AVLTree<F extends Comparable<F>> extends BinaryTree<F> {  
    // BinaryNode<F> theTree;
 
    @Override
    public void add (F toInsert)
    {
        // ...     
    }
}
 
public class Main {
    public static void main (String[] args) {}
}

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