using System;

​

class Base { }

class Sub : Base { }

class SubSub : Sub { }

public class Program

{

    public static void Main()

    {

        SubSub a = new SubSub();

​

        if (a is SubSub) { Console.WriteLine("a is SubSub"); } 

            // True

        if (a is Sub) { Console.WriteLine("a is Sub"); }    

            // True

        if (a is Base) { Console.WriteLine("a is Base"); }   

            // True

​

        a = null;

        if (a is SubSub) { /* ... */ } 

            // False / NULL

    }

}