using System.Collections.Generic;       

public class Program {

    public static void Main(){}

    public static IList<IGreeter> Local() {

        return ConcreteLocal();

    }

    public static IList<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 { }