using System;

public class Program

{

    public static void Main()

    {

        var t2 = new T2{P1="2"};

        T1 t1 = t2;

        t1.P1 = "1";

        Console.WriteLine(t2.P1 + " " + t1.P1 + " " + ((T2)t1).P1);

    }

}

​

class T1

{

    public string P1 {get; set;}    

}

​

class T2 : T1

{

    new public string P1 {get; set;}    

}