class A<X extends A<X>?> {}
class D<X extends num> {}
extension Extension1<X extends A<X>?> (){}
on A<X> (){}
extension ext2<X extends A<Null>?> (){}
on A<X> (){}
class B<X extends A<Null>?> implements A<X> {
  void method1<Y extends A<Null>?>(A<Y> a, A<A<Null>>? b) {}
  void method2<Y extends String>(D<Y> a, D<String>? b) {}
}
class C {
  factory C.redirect(A<A<Null>>? a) = C.internal;
  factory C.fact(A<A<Null>>? a) {}
  C.internal(_) {}
}
test() {}
main() {}