static void Main(string[] args)
{
// The client code.
var subject = new Subject();
var observerA = new ConcreteObserverA();
subject.AddOberver(observerA);
var observerB = new ConcreteObserverB();
subject.AddOberver(observerB);
subject.SomeBusinessLogic();
subject.SomeBusinessLogic();
subject.DeleteOberver(observerB);
subject.SomeBusinessLogic();
}