static void Main(string[] args)
{
var subject = new Subject();
var observer1 = new Observer1();
var observer2 = new Observer2();
subject.Attach(observer1);
subject.Attach(observer2);
subject.NotifyChange("Test change state 1");
subject.Detach(observer2);
subject.NotifyChange("Test change state 2");
Console.ReadLine();
}