library test;

abstract class A {
  int? get x;
}

abstract class B {
  int? get x;
}

abstract class C {
  num? get x;
}

abstract class D {
  double? get x;
}

class E extends A implements B {
  var x;
}

class F extends A implements C {
  var x;
}

class G extends A implements D {
  var x;
}

class H extends C implements D {
  var x;
}

main() {}