using System;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        var dict = new SortedDictionary<string, string>();

        dict.Add("Æ", "qwerty");

        Console.WriteLine(dict["AE"]); // outputs "qwerty"

        dict.Add("AE", ""); // [System.ArgumentException: An entry with the same key already exists.]

    }

}