using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public static void Main()

    {

        IEnumerable<string> oldVersions = new List<string>

        {

            "Hello"     ,

            "World",

            "Hello"

        };

        IEnumerable<string> newVersions= new List<string>{

            "World"

        };

        var temp = oldVersions.Except(newVersions);

        foreach (var item in temp){

            Console.WriteLine(item);

        }

    }

}