using System;

using System.Linq;

using System.Collections.Generic;

​

public class Program

{

    public static void Main()

    {

        List<int> input = new List<int> {1, 1, 2, 2, 3, 4};

        var res = new List<int>();

        foreach (int s in input.Where(s => 

                   { 

                       Console.WriteLine("lambda: s=" + s);

                       Console.WriteLine("lambda: " + s + " contained in res? " + res.Contains(s));

                       return !res.Contains(s);

                   }))

        {

            res.Add(s);

            Console.WriteLine("loop: " + s + " added to res");

            Console.WriteLine();

        }               

    }

}