class G12 {

/*
  interface Collection {
    boolean contains( Object o );
    boolean containsAll( Collection c );
    boolean removeAll( Collection c );
    boolean retainAll( Collection c );
    // etc.
  }
*/

  interface Collection<E> {
    boolean contains( Object o );

    boolean containsAll( Collection<?> c );
    boolean removeAll( Collection<?> c );
    boolean retainAll( Collection<?> c );
    
    // <T> boolean containsAll( Collection<T> c );
    // <T> boolean removeAll( Collection<T> c );
    // <T> boolean retainAll( Collection<T> c );
    
    // etc.
  }

}