using System;

using System.Linq;

​

​

​

static public class Program

{

    static IEnumerable<int> Where(

        this int[] ints, Func<int, bool> gauntlet)

    {

        Console.WriteLine("My Where()");

        foreach(int idx in ints)

            if (gauntlet(idx))

                yield return idx;

    }

    public static void Main()

    {

        int[] numbers = new[] { 3, 1, 4, 1, 5 };

        var result1 = 

            from n in numbers

            where n < 5

            select n;

        foreach(int idx in result1) {

            Console.WriteLine(idx);

        }

    }   

​

}