using System;

using System.Collections;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public static void Main()

    {       

        List<int> lefts = Enumerable.Range(1, 10).ToList();//.Select(x => x * x);

        List<int> rights = Enumerable.Range(5, 15).ToList();//.Select(x => x * x);

    var q=  from l in lefts

                join r in rights on l equals r into collect

            from res in collect.DefaultIfEmpty()

        select new {X=l,Y=res}  ;

          System.Console.WriteLine(q);

​

        foreach(var a in q)

        {

                    System.Console.WriteLine(a.X.ToString() +": "+ a.Y.ToString());

        }

    }

}