Interface

gistfile1.cs

namespace ConsoleApplication6
{
    using System;

    class Program
    {
        static void Main(string[] args)
        {
            var a = new MyClass();

            var b = a as IA;
            var c = b as IB;

            b.M1();            
            c.B1();
        }
    }

    class MyClass : IA, IB
    {

        public void M1()
        {
            Console.WriteLine("IA M1");
        }

        public void B1()
        {
            Console.WriteLine("IB B1");
        }
    }

    interface IA
    {
        void M1();
    }

    interface IB
    {

        void B1();
    }
}