using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public static void Main()

    {

        var xs = new int?[] { 1, null, 2 };

        var ys = new int?[] { 1, null, 2 };

        foreach (var x in xs.Join(ys, x => x, y => y, (x, y) => x))

            Console.WriteLine("Yield x = " + x);

    }

}