static void Main(string[] args)
{
Subject s1 = new Subject();
IObserver o1 = new Observer1();
IObserver o2 = new Observer2();
s1.register(o1);
s1.register(o2);
s1.Flag = 5;
s1.Flag = 25;
s1.unregister(o1);
s1.Flag = 50;
/*List<string> lista1 = new List<string>() { "1", "2", "3", "4" };
* List<string> lista2 = new List<string>() { "1", "2", "3", "6" };
* List<string> except = lista1.exceptAll(lista2);
*
* except.ForEach(Console.WriteLine);
*/
Console.ReadLine();
}