public static void Start()
        {
            LinkedIn observable = new LinkedIn();

            UnemployedEngineer jack   = new UnemployedEngineer(observable, "jack");
            UnemployedHr       emily  = new UnemployedHr(observable, "emily");
            UnemployedEngineer angely = new UnemployedEngineer(observable, "angely");
            UnemployedHr       john   = new UnemployedHr(observable, "john");

            observable.NewJobsAvailabel();

            observable.UnRegisterObserver(jack);
            observable.UnRegisterObserver(angely);

            observable.NewJobsAvailabel();

            observable.RegisterObserver(jack);
            observable.RegisterObserver(angely);

            observable.NewJobsAvailabelPullMode();
        }