using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public static void Main()

    {

        var conflicts = new List<Tuple<string, string>>();

        conflicts.Add(new Tuple<string, string>("Maths", "English"));

        conflicts.Add(new Tuple<string, string>("Science", "French"));

        conflicts.Add(new Tuple<string, string>("French", "Science"));

        conflicts.Add(new Tuple<string, string>("English", "Maths"));

        RemoveDupes(conflicts);

        foreach(var i in conflicts) Console.WriteLine(i.Item1 + " " + i.Item2);

    }

    public static void RemoveDupes(List<Tuple<string, string>> collection){

        var duplicates = collection

            // indescriminate which value comes first

            .Select((x, i) => new{ Item= new Tuple<string,string>(x.Item2.IsGreaterThan(x.Item1) ? x.Item2 : x.Item1, 

                                                                  x.Item2.IsGreaterThan(x.Item1) ? x.Item1 : x.Item2), Index = i})

            // group on the now indescrimitate values

            .GroupBy(x => x.Item)

            // find duplicates

            .Where(x => x.Count() > 1)

            .Select(x => new {Items = x, Count=x.Count()})

            // select all indexes but first

            .SelectMany( x =>

                x.Items.Select( b => b)

                       .Zip(Enumerable.Range( 1, x.Count ),

                            ( j, i ) => new { Item = j, RowNumber = i }

                )

            ).Where(x => x.RowNumber != 1);

        foreach(var item in duplicates){

            collection.RemoveAt(item.Item.Index);

        }

    }

}

​

public static class Ext{

    public static bool IsGreaterThan(this string val, string compare){

        return val.CompareTo(compare) == 1;

    }

}