using System;

using System.Collections;

using System.Linq;

public class Program

{

    public static void Main()

    {

        int[] set1 = { 1,2,3,4,6,9,13,25};

        int[] set2 = { 1,2,3,6,9,25,29,39};

        // https://docs.microsoft.com/en-us/dotnet/api/system.linq.queryable.except?view=netcore-2.1

        var delta1  = set1.AsQueryable().Except(set2);

        foreach(var delta in delta1)

        {

            Console.WriteLine(delta);

        }

        Console.WriteLine("**************");

        Console.WriteLine("");

        // https://docs.microsoft.com/en-us/dotnet/api/system.linq.queryable.groupjoin?view=netcore-2.1

        var query = set1.GroupJoin(set2, s1 => s1, s2 => s2, ( s1, s2) => new {s1 = s1, s2 = s2}).SelectMany( x => x.s2.DefaultIfEmpty(), (s1, s2) => new { s1, s2}).Where(s => s.s2 == 0);

        foreach(var result in query) 

        {

            Console.WriteLine(result);

        }

    }

}