public static void Main(string[] Args)
{
MyClass aaa = new ClassA();
MyClass bbb = new ClassB();
aaa.A(); // prints MyClass.A
aaa.B(); // prints MyClass.B
(aaa as ClassA).A(); // prints AttachmentA.A
(aaa as ClassA).B(); // prints MyClass.B
bbb.A(); // prints MyClass.A
bbb.B(); // prints MyClass.B
(bbb as ClassB).A(); // prints AttachmentB.A + MyClass.A
(bbb as ClassB).B(); // prints AttachmentB.B
}