abstract class Super {
  abstract SuperInner<?> a();

  abstract static class SuperInner<T extends SuperInner<T>> {
    abstract T b();

    abstract Super c();
  }
}

abstract class Sub extends Super {
  // It is significant that this method specializes the
  // return type. If this returns SuperInner, no crash happens.
  @Override
  abstract SubInner<?> a();

  abstract static class SubInner<S extends SubInner<S>> extends Super.SuperInner<S> {
    // Crashes with this overridden method and passes without it.
    @Override
    abstract Super c();
  }
}