diff --git a/MainWindow.axaml b/MainWindow.axaml
index 3198a2d..a38647d 100644
--- a/MainWindow.axaml
+++ b/MainWindow.axaml
@@ -173,6 +173,7 @@
                                 </Button>
                                 <Button HorizontalAlignment="Stretch" MinWidth="240"
                                         HorizontalContentAlignment="Center" x:Name="BtnCombineDifference"
+                                        Click="BtnCombineDifference_OnClick"
                                         Margin="0,0,0,10">
                                     <StackPanel Orientation="Horizontal">
                                         <LucideIcon Kind="SquaresSubtract" Width="36" Height="36" />
diff --git a/MainWindow.axaml.cs b/MainWindow.axaml.cs
index 2628a48..981dc46 100644
--- a/MainWindow.axaml.cs
+++ b/MainWindow.axaml.cs
@@ -1,7 +1,6 @@
 using System;
 using System.Collections.Generic;
 using System.Diagnostics;
-using System.IO;
 using System.Threading.Tasks;
 using Avalonia.Controls;
 using Avalonia.Interactivity;
@@ -197,14 +196,14 @@ public partial class MainWindow : Window
         progressWindow.Show(_instance);
 
         var processor = new CombineAddresses(progressWindow);
-        var result = await processor.Perform(address_list);
+        //var result = await processor.Perform(address_list);
 
 
         progressWindow.Close();
-        File.WriteAllText(OpenSettingsSaveAsDialog().Result,
-            new CsvBuilder(
-                "refsid,anrede,titel,vorname,adel,name,namezus,anredzus,strasse,strasse2,plz,ort,land,pplz,postfach,name1,name2,name3,name4,name5,funktion,funktion2,abteilung,funktionad,lastupdate",
-                result).BuildKas());
+        //File.WriteAllText(OpenSettingsSaveAsDialog().Result,
+        //new CsvBuilder(
+        //"refsid,anrede,titel,vorname,adel,name,namezus,anredzus,strasse,strasse2,plz,ort,land,pplz,postfach,name1,name2,name3,name4,name5,funktion,funktion2,abteilung,funktionad,lastupdate",
+        //result).BuildKas());
     }
 
     private async Task<string> OpenSettingsSaveAsDialog()
@@ -241,6 +240,24 @@ public partial class MainWindow : Window
         }
     }
 
+    private async void StartDifference(List<KasAddressList> address_lists, int owner_id)
+    {
+        var progressWindow = new ProgressWindow();
+
+        progressWindow.Show(_instance);
+
+        var processor = new CombineAddresses(progressWindow);
+        var result = await processor.Perform(address_lists, "difference");
+
+        result.owner_id = owner_id;
+        Settings._instance.addressSets.addresses.Add(result);
+        Settings.Save();
+        progressWindow.Close();
+
+
+        //new ResultWindow(result, addresSetID).Show();
+    }
+
     private void BtnSettingsAddCustomer_OnClick(object? sender, RoutedEventArgs e)
     {
         Settings._instance.customers.customers.Add(new Customer());
@@ -399,7 +416,7 @@ public partial class MainWindow : Window
         foreach (var k in Settings._instance.addressSets.addresses)
         foreach (var customer in Settings._instance.customers.customers)
             if (customer.ID == k.owner_id && customer.ID == customer_id)
-                LstCustomerAdressSets.Items.Add(k.ID + " - " + k.Name);
+                LstCustomerAdressSets.Items.Add(k.ID + " - " + k.Name + "(" + k.KasPersons.Count + " Einträge)");
     }
 
     private void LstCustomerAdressSets_OnSelectionChanged(object? sender, SelectionChangedEventArgs e)
@@ -474,4 +491,14 @@ public partial class MainWindow : Window
                     MessageBox.Show(this, "Unknown Error: " + ex.Message, "Error");
                 }
     }
+
+    private void BtnCombineDifference_OnClick(object? sender, RoutedEventArgs e)
+    {
+        var list = new List<KasAddressList>();
+        foreach (var item in LstCustomerAdressSets.SelectedItems)
+            list.Add(Settings._instance.addressSets.GetAddressSetByID(
+                Convert.ToInt32(item.ToString().Split(" - ")[0])));
+
+        StartDifference(list, Convert.ToInt32(LstCustomers.SelectedItem.ToString().Split(" - ")[0]));
+    }
 }
\ No newline at end of file
diff --git a/Tasks/CombineAddresses.cs b/Tasks/CombineAddresses.cs
index 8fc17c0..d9fc293 100644
--- a/Tasks/CombineAddresses.cs
+++ b/Tasks/CombineAddresses.cs
@@ -1,5 +1,7 @@
 using System;
 using System.Collections.Generic;
+using System.Linq;
+using System.Threading;
 using System.Threading.Tasks;
 using Avalonia.Threading;
 
@@ -14,84 +16,38 @@ public class CombineAddresses
         _progress = progressWindow;
     }
 
-    public async Task<KasAddressList> Perform(List<KasAddressList> address_lists)
+    public async Task<KasAddressList> Perform(List<KasAddressList> address_lists, string type)
     {
-        KasAddressList result = new("Ergebnis_" + DateTime.Now.ToString("ddMMyy_HHmmss"));
-        await Task.Run(async () =>
+        var res = await Task.Run(async () =>
         {
-            for (var i = 0; i < address_lists.Count; i++)
-                if (i == 0)
-                    lock (result)
-                    {
-                        result = address_lists[i];
-                    }
-                else
-                    lock (result)
-                    {
-                        result = Merge(result, address_lists[i], i + 1, address_lists.Count).Result;
-                    }
+            if (type == "difference") return Difference(address_lists);
+
+            return null;
         });
-        return result;
+
+
+        return res.Result;
+
+
+        // KasAddressList result = new("Ergebnis_" + DateTime.Now.ToString("ddMMyy_HHmmss"));
+        // await Task.Run(async () =>
+        // {
+        //     for (var i = 0; i < address_lists.Count; i++)
+        //         if (i == 0)
+        //             lock (result)
+        //             {
+        //                 result = address_lists[i];
+        //             }
+        //         else
+        //             lock (result)
+        //             {
+        //                 result = Merge(result, address_lists[i], i + 1, address_lists.Count).Result;
+        //             }
+        // });
+        // return result;
+        return null;
     }
 
-    private async Task<KasAddressList> Merge(KasAddressList first, KasAddressList second, int num, int total)
-    {
-        foreach (var sec in second.KasPersons)
-        {
-            var is_new = true;
-            foreach (var fi in first.KasPersons)
-            {
-                if (fi.refsid == sec.refsid)
-                {
-                    is_new = false;
-                    break;
-                }
-
-                if (fi.name == sec.name &&
-                    fi.anrede == sec.anrede &&
-                    fi.anredzus == sec.anredzus &&
-                    fi.namezus == sec.namezus &&
-                    fi.titel == sec.titel &&
-                    fi.adel == sec.adel &&
-                    fi.strasse == sec.strasse &&
-                    fi.strasse2 == sec.strasse2 &&
-                    fi.vorname == sec.vorname &&
-                    fi.ort == sec.ort &&
-                    fi.land == sec.land &&
-                    fi.plz == sec.plz &&
-                    fi.pplz == sec.pplz &&
-                    fi.funktion == sec.funktion &&
-                    fi.funktion2 == sec.funktion2 &&
-                    fi.funktionad == sec.funktionad &&
-                    fi.abteilung == sec.abteilung &&
-                    fi.postfach == sec.postfach &&
-                    fi.name1 == sec.name1 &&
-                    fi.name2 == sec.name2 &&
-                    fi.name3 == sec.name3 &&
-                    fi.name4 == sec.name4 &&
-                    fi.name5 == sec.name5)
-                {
-                    is_new = false;
-                    break;
-                }
-            }
-
-            if (is_new) first.KasPersons.Add(sec);
-            var subperc = second.KasPersons.IndexOf(sec) / second.KasPersons.Count;
-            var percent = (num + (double)subperc) / total * 100;
-            await Dispatcher.UIThread.InvokeAsync(() =>
-            {
-                if (is_new)
-                    _progress.AddToLog($"Person mit refsid {sec.refsid} ergänzt");
-                else
-                    _progress.AddToLog($"Person mit refsid {sec.refsid} bereits vorhanden");
-
-                _progress.ChangePercentage(percent);
-            });
-        }
-
-        return first;
-    }
 
     /// <summary>
     ///     Returns true if the addresses are the same.
@@ -132,11 +88,44 @@ public class CombineAddresses
         return false;
     }
 
-    public async Task<KasAddressList> Difference()
+    public async Task<KasAddressList> Difference(List<KasAddressList> address_lists,
+        DifferenceProgress? progress = null)
     {
-        return null;
+        if (address_lists == null || address_lists.Count == 0)
+            return new KasAddressList("difference");
+
+        progress ??= new DifferenceProgress
+        {
+            TotalPersons = address_lists.Sum(l => l.KasPersons.Count),
+            ComparedPersons = 0
+        };
+
+        // Vereinigung aller Listen außer der ersten
+        var restUnion = new List<KasPerson>();
+        for (var i = 1; i < address_lists.Count; i++)
+            restUnion.AddRange(address_lists[i].KasPersons);
+
+        var result = new KasAddressList("difference");
+
+        foreach (var person in address_lists[0].KasPersons)
+        {
+            var isDouble = restUnion.Any(p => CompareAddresses(person, p));
+            if (!isDouble)
+                result.KasPersons.Add(person);
+
+            progress.Increment();
+            if (progress.LogAction != null)
+            {
+                var logMessage =
+                    $"Person mit refsid {person.refsid} verglichen mit {restUnion.Count} Personen des Restes.";
+                await Dispatcher.UIThread.InvokeAsync(() => progress.LogAction?.Invoke(logMessage));
+            }
+        }
+
+        return result;
     }
 
+
     public async Task<KasAddressList> Union()
     {
         return null;
@@ -156,4 +145,80 @@ public class CombineAddresses
     {
         return null;
     }
+
+
+    // private async Task<KasAddressList> Merge(KasAddressList first, KasAddressList second, int num, int total)
+    // {
+    //     foreach (var sec in second.KasPersons)
+    //     {
+    //         var is_new = true;
+    //         foreach (var fi in first.KasPersons)
+    //         {
+    //             if (fi.refsid == sec.refsid)
+    //             {
+    //                 is_new = false;
+    //                 break;
+    //             }
+    //
+    //             if (fi.name == sec.name &&
+    //                 fi.anrede == sec.anrede &&
+    //                 fi.anredzus == sec.anredzus &&
+    //                 fi.namezus == sec.namezus &&
+    //                 fi.titel == sec.titel &&
+    //                 fi.adel == sec.adel &&
+    //                 fi.strasse == sec.strasse &&
+    //                 fi.strasse2 == sec.strasse2 &&
+    //                 fi.vorname == sec.vorname &&
+    //                 fi.ort == sec.ort &&
+    //                 fi.land == sec.land &&
+    //                 fi.plz == sec.plz &&
+    //                 fi.pplz == sec.pplz &&
+    //                 fi.funktion == sec.funktion &&
+    //                 fi.funktion2 == sec.funktion2 &&
+    //                 fi.funktionad == sec.funktionad &&
+    //                 fi.abteilung == sec.abteilung &&
+    //                 fi.postfach == sec.postfach &&
+    //                 fi.name1 == sec.name1 &&
+    //                 fi.name2 == sec.name2 &&
+    //                 fi.name3 == sec.name3 &&
+    //                 fi.name4 == sec.name4 &&
+    //                 fi.name5 == sec.name5)
+    //             {
+    //                 is_new = false;
+    //                 break;
+    //             }
+    //         }
+    //
+    //         if (is_new) first.KasPersons.Add(sec);
+    //         var subperc = second.KasPersons.IndexOf(sec) / second.KasPersons.Count;
+    //         var percent = (num + (double)subperc) / total * 100;
+    //         await Dispatcher.UIThread.InvokeAsync(() =>
+    //         {
+    //             if (is_new)
+    //                 _progress.AddToLog($"Person mit refsid {sec.refsid} ergänzt");
+    //             else
+    //                 _progress.AddToLog($"Person mit refsid {sec.refsid} bereits vorhanden");
+    //
+    //             _progress.ChangePercentage(percent);
+    //         });
+    //     }
+    //
+    //     return first;
+    // }
+}
+
+public class DifferenceProgress
+{
+    public int TotalPersons { get; set; } // Gesamtzahl der zu prüfenden Personen
+    public int ComparedPersons { get; set; } // Schon verglichene Personen
+
+    public double Percentage => TotalPersons == 0 ? 0 : (double)ComparedPersons / TotalPersons * 100;
+
+    public Action<string>? LogAction { get; set; } // z.B. Dispatcher-UI-Callback
+
+    public void Increment()
+    {
+        var comparedPersons = ComparedPersons;
+        Interlocked.Increment(ref comparedPersons);
+    }
 }
\ No newline at end of file