using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text.RegularExpressions;

public class Test
{
	public static Regex rx = new Regex(@"^(TC_)_?(\d+).*", RegexOptions.Compiled);
	public class FilePathComparer : IEqualityComparer<string>
	{
	    public bool Equals(string x, string y)
	    {
	        return rx.Replace(x, "$1$2") == rx.Replace(y, "$1$2");
	    }
	    public int GetHashCode(string s)
	    {
	        return rx.Replace(s,"$1$2").GetHashCode();
	    }
	}
	public static void Main()
	{
		var FileNames_List_Jetzt_Dateien = new List<string> { "TC__6493_8exp","TC__6494_8exp","TC__6495_8exp"};
		var TEST_FÄLLE = new List<string> { "TC_6493","TC_6494","TC_6495"};
    	var intersected = FileNames_List_Jetzt_Dateien.Intersect(TEST_FÄLLE, new FilePathComparer());
        foreach (var s in intersected)
        	Console.WriteLine(s);
	}
}