// @dart = 2.9
class A1<T> {}

extension A2<T> on A1<T> {
  A1<T> method1<S extends T>() {}
  A1<T> method2<S extends A1<T>>(S o) {}
}

extension A3<T extends A1<T>> on A1<T> {}

extension A4<T> on A1<T> {
  method<T>() {}
}

main() {}