void Start()
        {
            Debug.Log("Start Observer!");
            var subj = new Subject();
            var o1   = new ConcreteObserverA();

            subj.attach(o1);

            var o2 = new ConcreteObserverB();

            subj.attach(o2);

            StartCoroutine(subj.someBusinessLogic());

            //subj.detach(o2);

            //StartCoroutine(subj.someBusinessLogic());
        }