class Foo {
    abstract static class Animal<A extends Animal<A>> {
          abstract A copyAnimal(A animal);
    }
 
    static class Duck<D extends Duck<D>> extends Animal<D> {
      void quack() {}
 
      D copyAnimal(D duck) {
        duck.quack();
        return duck;
      }
    }
 
    static class Mallard extends Duck<Mallard> {
      Mallard copyAnimal(Mallard duck) {
        duck.quack();
        return duck;
      }
    }
 
    public static void main(String[] args) {}
}
 

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