using System;

using System.Collections.Generic;

using System.Linq;

​

 public static class Extensions

 {

     public static void AddDistinct<T>(this IList<IEnumerable<T>> list, IEnumerable<T> s)

     {

         foreach (var x in list)

         {

             if (x.SequenceEqual(s))

             {

                 return;

             }

         }

         list.Add(s);

     }

 }

​

public class Program

{

    public static void Main()

    {

        var x = new List<List<int>>();

        x.AddDistinct(new List<int>{ 1, 2, 3});

    }

}