using System;

//using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        Console.WriteLine("Hello World");

        Novels n = new Novels();

        Books b= n;     

        //Co-Variance

        IDemoCoVar<Novels> xN= new X<Novels>();

        IDemoCoVar<Books> xB=xN;

        //Contra-Variance

        IDemoContraVar<Books> vB=new X<Books>();

        IDemoContraVar<Novels> vN=vB;

    }

}

public class Books

{

}

public class Novels:Books

{

}

public class X<T>:IDemoCoVar<T>,IDemoContraVar<T>

{

}

public interface IDemoCoVar<out T>

{

}

public interface IDemoContraVar<in T>

{

}