static void Main(string[] args)
{
var subject = new ConcreteSubject();
var observer1 = new ConcreteObserver1();
subject.Attach(observer1);
var observer2 = new ConcreteObserver2();
subject.Attach(observer2);
var observer3 = new ConcreteObserver3();
subject.Attach(observer3);
subject.BusinessLogic();
subject.BusinessLogic();
subject.Detach(observer3);
subject.BusinessLogic();
}