library test;

abstract class A {
  void set x(int? value);
}

class B {
  void set x(int? value) {}
}

class C extends A {
  var x;
}

class D extends B {
  var x;
}

class E implements A {
  var x;
}

class F implements B {
  var x;
}

class G extends Object with B {
  var x;
}

main() {}