static void Main(string[] args)
{
var subject = new Subject();
var observerA = new ConcreteObserverA();
subject.Attach(observerA);
var observerB = new ConcreteObserverB();
subject.Attach(observerB);
subject.SomeBusinessLogic();
subject.SomeBusinessLogic();
subject.Dettach(observerB);
subject.SomeBusinessLogic();
}