using System;

public class Program

{

    public static void Main()

    {

        var a = new A1();

        a.m1();

        a.m2();

        var a2 = new A2();

        a2.m3();

        a2.m4();

    }

}

​

public static class ExtensoesA1

{

    public static void Baka(this A1 a1)

    {

        Console.WriteLine("I work");

    }

}

​

public class A1

{

    public void m1()

    {

        this.Baka();

    }

    public void m2()

    {

        Baka();

    }

}

​

public class A2 : A1

{

    public void m3()

    {

        this.Baka();

    }

    public void m4()

    {

        Baka();

    }

}