using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public static void Main()

    {

        var a = new List<String> { "a" }.Append("b");

        var b = new List<String> { "a" }.Concat(new [] { "b" });

        Console.WriteLine("append returns " + a.GetType().Name);

        Console.WriteLine("concat reutrns " + b.GetType().Name);

    }

}