using System.Collections.Generic;

​

public class Program

{

    public static void Main()

    {

    }

    public static IEnumerable<IGreeter> Local()

    {

        return ConcreteLocal();

    }

    public static IEnumerable<IGreeter> Foreigner()

    {

        return ConcreteForeigner();

    }

    public static IList<Hello> ConcreteLocal()

    {

        return new List<Hello>();

    }

    public static IList<Ciao> ConcreteForeigner()

    {

        return new List<Ciao>();

    }

}

​

​

public interface IGreeter

{

}

​

public class Hello : IGreeter

{

}

​

public class Ciao : IGreeter

{

}