let
  class C
  {
    var a := 0
    method m() : int = self.a
  }
  class D extends C
  {
    var b := 9
    /* Override C.m().  */
    method m() : int = self.a + self.b
  }
  var d : D := new D
  /* Valid upcast due to inclusion polymorphism.  */
  var c : C := d
  in
    c.a := 42;
    /* Note that accessing `c.b' is not allowed, since `c' is
         statically known as a `C', even though it is actually a `D'
         at run time.  */
    let
      /* Polymorphic call.  */
    var res := c.m()
    in
      print_int(res);
      print("\n")
    end
end