diff --git a/csharp/App/Backend/DataTypes/Methods/Credentials.cs b/csharp/App/Backend/DataTypes/Methods/Credentials.cs
index 1a8e24703..2e29149b1 100644
--- a/csharp/App/Backend/DataTypes/Methods/Credentials.cs
+++ b/csharp/App/Backend/DataTypes/Methods/Credentials.cs
@@ -8,12 +8,14 @@ public static class CredentialsMethods
 {
     public static Session? Login(this Credentials credentials)
     {
-        if (credentials.Username.IsNullOrEmpty() || credentials.Password.IsNullOrEmpty())
+        var (username, password) = credentials;
+        
+        if (username.IsNullOrEmpty() || password.IsNullOrEmpty())
             return null;
 
-        var user = Db.GetUserByEmail(credentials.Username);
+        var user = Db.GetUserByEmail(username);
 
-        if (user is null || !user.VerifyPassword(credentials.Password))
+        if (user is null || !user.VerifyPassword(password))
             return null;
 
         var session = new Session(user);
diff --git a/csharp/App/Backend/DataTypes/Methods/Folder.cs b/csharp/App/Backend/DataTypes/Methods/Folder.cs
index 321aca9eb..f643856ff 100644
--- a/csharp/App/Backend/DataTypes/Methods/Folder.cs
+++ b/csharp/App/Backend/DataTypes/Methods/Folder.cs
@@ -21,7 +21,9 @@ public static class FolderMethods
     
     public static IEnumerable<Folder> DescendantFolders(this Folder parent)
     {
-        return parent.Traverse(ChildFolders);
+        return parent
+              .TraverseDepthFirstPreOrder(ChildFolders)
+              .Skip(1); // skip self
     }
 
     public static Boolean IsDescendantOf(this Folder folder, Folder ancestor)
diff --git a/csharp/App/Backend/DataTypes/Methods/User.cs b/csharp/App/Backend/DataTypes/Methods/User.cs
index b7498ccfe..e541dcdd7 100644
--- a/csharp/App/Backend/DataTypes/Methods/User.cs
+++ b/csharp/App/Backend/DataTypes/Methods/User.cs
@@ -73,7 +73,9 @@ public static class UserMethods
 
     public static IEnumerable<User> DescendantUsers(this User parent)
     {
-        return parent.Traverse(ChildUsers);
+        return parent
+              .TraverseDepthFirstPreOrder(ChildUsers)
+              .Skip(1); // skip self
     }
 
     public static Boolean IsDescendantOf(this User user, User ancestor)
diff --git a/csharp/App/Backend/Program.cs b/csharp/App/Backend/Program.cs
index d32326b7a..e7500ff1a 100644
--- a/csharp/App/Backend/Program.cs
+++ b/csharp/App/Backend/Program.cs
@@ -1,4 +1,3 @@
-using System.Reactive.Linq;
 using InnovEnergy.App.Backend.Database;
 using Microsoft.OpenApi.Models;
 
@@ -8,7 +7,6 @@ public static class Program
 {
     public static void Main(String[] args)
     {
-        
         Db.CreateFakeRelations();
 
         var builder = WebApplication.CreateBuilder(args);
diff --git a/csharp/Lib/Utils/TreeTraversal.cs b/csharp/Lib/Utils/TreeTraversal.cs
new file mode 100644
index 000000000..4fef44baf
--- /dev/null
+++ b/csharp/Lib/Utils/TreeTraversal.cs
@@ -0,0 +1,147 @@
+namespace InnovEnergy.Lib.Utils;
+
+public static class TreeTraversal
+{
+    // public static IEnumerable<T> TraverseDepthFirstPreOrder<T>(this T root, Func<T, IEnumerable<T>> getChildren)
+    // {
+    //     var stack = new Stack<IEnumerator<T>>();
+    //
+    //     var iterator = root.AsSingleEnumerator();
+    //
+    //     while (true)
+    //     {
+    //         while (iterator.MoveNext())
+    //         {
+    //             yield return iterator.Current;
+    //
+    //             iterator = getChildren(iterator.Current).GetEnumerator();
+    //             stack.Push(iterator);
+    //         }
+    //
+    //         iterator.Dispose();
+    //         if (stack.Count == 0) 
+    //             yield break;
+    //
+    //         iterator = stack.Pop();
+    //     }
+    //     
+    // }
+
+    public static IEnumerable<T> TraverseDepthFirstPreOrder<T>(this T root, Func<T, IEnumerable<T>> getChildren)
+    {
+        return Traverse(root, 
+                        getChildren, 
+                        branchOpen: true, 
+                        branchClose: false, 
+                        leaf: true);
+    }
+
+    public static IEnumerable<T> TraverseDepthFirstPostOrder<T>(this T root, Func<T, IEnumerable<T>> getChildren)
+    {
+        return Traverse(root, 
+                        getChildren, 
+                        branchOpen: false, 
+                        branchClose: true, 
+                        leaf: true);
+    }
+    
+    public static IEnumerable<T> TraverseLeaves<T>(this T root, Func<T, IEnumerable<T>> getChildren)
+    {
+        return Traverse(root, 
+                        getChildren, 
+                        branchOpen: false, 
+                        branchClose: true, 
+                        leaf: false);
+    }
+
+
+    private static IEnumerable<T> Traverse<T>(T root,
+                        Func<T, IEnumerable<T>> getChildren,
+                                        Boolean branchOpen,
+                                        Boolean branchClose,
+                                        Boolean leaf)
+    {
+        // the if-checks on the constant booleans are
+        // almost free because of modern branch predictors
+        
+        var stack = new Stack<IEnumerator<T>>();
+        var it    = root.AsSingleEnumerator();
+        it.MoveNext();
+
+        while (true)
+        {
+            //////// going down //////// 
+
+            while (true)
+            {
+                var cit = getChildren(it.Current).GetEnumerator();
+
+                if (cit.MoveNext()) // node has children, must be a branch
+                {
+                    if (branchOpen)
+                        yield return it.Current;
+
+                    stack.Push(it);
+                    it = cit;
+                }
+                else // no children, hence a leaf
+                {
+                    var node = it.Current;
+
+                    if (leaf)
+                        yield return node;
+
+                    if (!it.MoveNext())
+                        break; // no more siblings: goto parent
+                }
+            }
+
+            //////// going up //////// 
+
+            while (true)
+            {
+                it.Dispose();
+                if (stack.Count == 0) yield break; // we got to the bottom of the stack, were done
+
+                it = stack.Pop();
+
+                var node = it.Current;
+
+                if (branchClose)
+                    yield return node; // we've seen all its children: close the branch
+
+                if (it.MoveNext())
+                    break;
+            }
+        }
+    }
+
+
+    public static IEnumerable<T> TraverseBreadthFirst<T>(this T node, Func<T, IEnumerable<T>> getChildren)
+    {
+        var queue = new Queue<IEnumerator<T>>();
+    
+        var iterator = node.AsSingleEnumerator();
+        
+        while(true)
+        {
+            while (iterator.MoveNext())
+            {
+                yield return iterator.Current;
+    
+                iterator.Current
+                        .Apply(getChildren)
+                        .GetEnumerator()
+                        .Apply(queue.Enqueue);
+            }
+    
+            iterator.Dispose();
+    
+            if (queue.Count == 0)
+                yield break;
+            
+            iterator = queue.Dequeue();
+        }
+        
+    }
+}
\ No newline at end of file
diff --git a/csharp/Lib/Utils/Utils.cs b/csharp/Lib/Utils/Utils.cs
index 690d6abaa..c76476a35 100644
--- a/csharp/Lib/Utils/Utils.cs
+++ b/csharp/Lib/Utils/Utils.cs
@@ -1,4 +1,5 @@
 using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
 using System.Runtime.CompilerServices;
 using static System.Runtime.CompilerServices.MethodImplOptions;
 
@@ -6,6 +7,7 @@ namespace InnovEnergy.Lib.Utils;
 
 public static class Utils
 {
+    public static Boolean IsNull<T>([NotNullWhen(returnValue: false)] this T t) => t is null;
 
     public static IEnumerable<String> GetEnumStrings<T>(this T e) where T : Enum
     {
@@ -20,7 +22,7 @@ public static class Utils
     [DebuggerStepThrough][MethodImpl(AggressiveInlining)]
     public static T ConvertTo<T>(this IConvertible c) where T : IConvertible
     {
-        var t = typeof (T);
+        var t = typeof(T);
 
         var type = t.IsEnum
                  ? Enum.GetUnderlyingType(t)
@@ -50,13 +52,13 @@ public static class Utils
     [DebuggerStepThrough][MethodImpl(AggressiveInlining | AggressiveOptimization)]
     public static R Apply<T, R>(this T t, Func<T, R> f) => f(t);
 
-    [DebuggerStepThrough]
-    [MethodImpl(AggressiveInlining | AggressiveOptimization)]
+    
+    [DebuggerStepThrough][MethodImpl(AggressiveInlining | AggressiveOptimization)]
     public static R Apply<T1, T2, R>(this (T1 p1, T2 p2) t, Func<T1, T2, R> f) => f(t.p1, t.p2);
 
-    [DebuggerStepThrough]
-    [MethodImpl(AggressiveInlining | AggressiveOptimization)]
-    public static R Apply<T1, T2, T3, R>(this (T1 p1, T2 p2,  T3 p3) t, Func<T1, T2, T3, R> f) => f(t.p1, t.p2, t.p3);
+    
+    [DebuggerStepThrough][MethodImpl(AggressiveInlining | AggressiveOptimization)]
+    public static R Apply<T1, T2, T3, R>(this (T1 p1, T2 p2, T3 p3) t, Func<T1, T2, T3, R> f) => f(t.p1, t.p2, t.p3);
 
     [DebuggerStepThrough][MethodImpl(AggressiveInlining | AggressiveOptimization)]
     public static R ApplyOrDefault<T, R>(this T t, Func<T, R> f, R @default)
@@ -79,7 +81,7 @@ public static class Utils
              ? res
              : res + length;
     }
-    
+
     public static Decimal Modulo(this Decimal dividend, Decimal divisor)
     {
         var res = dividend % divisor;
@@ -89,111 +91,39 @@ public static class Utils
              : res + divisor;
     }
 
-    public static IEnumerable<T> Traverse<T>(this T root, Func<T, IEnumerable<T>> getChildren)
-    {
-        var stack = new Stack<IEnumerator<T>>();
-        var it    = root.AsSingleEnumerator();
-        it.MoveNext();
-
-        while (true)
-        {
-            //////// going down ////////
-
-            while (true)
-            {
-                var cit = getChildren(it.Current).GetEnumerator();
-
-                if (cit.MoveNext())  // node has children, must be a branch
-                {
-                    yield return it.Current;
-
-                    stack.Push(it);
-                    it = cit;
-                }
-                else // no children, hence a leaf
-                {
-                    var node = it.Current;
-
-                    yield return node;
-
-                    if (!it.MoveNext())
-                        break; // no more siblings: goto parent
-                }
-            }
-
-            //////// going up ////////
-
-            while (true)
-            {
-                it.Dispose();
-                if (stack.Count == 0)
-                    yield break; // we got to the bottom of the stack, were done
-
-                it = stack.Pop();
-
-                if (it.MoveNext())
-                    break;
-            }
-        }
-
-    }
 
     public static Int32 Clamp(this Int32 value, Int32 minValue, Int32 maxValue)
     {
         var clamped = Math.Min(maxValue, value);
         clamped = Math.Max(minValue, clamped);
-        
+
         return clamped;
     }
-    
+
     public static Double Clamp(this Double value, Double minValue, Double maxValue)
     {
         var clamped = Math.Min(maxValue, value);
         clamped = Math.Max(minValue, clamped);
-        
+
         return clamped;
     }
-    
-    
+
+
     public static Decimal Clamp(this Decimal value, Decimal minValue, Decimal maxValue)
     {
         var clamped = Math.Min(maxValue, value);
         clamped = Math.Max(minValue, clamped);
-        
+
         return clamped;
     }
 
-
-#pragma warning disable 8714
-
-    public static async Task<R> ApplyOrDefault<T, R>(this T t, Func<T, Task<R>> f, R @default)
-    {
-        try
-        {
-            return await f(t);
-        }
-        catch
-        {
-            return @default;
-        }
-    }
-
-    public static R ValueOrDefault<T, R>(this Dictionary<T, R> dict, T key, R defaultValue)
+    public static R ValueOrDefault<T, R>(this Dictionary<T, R> dict, T key, R defaultValue) where T : notnull
     {
         return dict.TryGetValue(key, out var value)
-            ? value
-            : defaultValue;
+             ? value
+             : defaultValue;
     }
 
-
-    public static Dictionary<K, V> CombineDicts<K,V>(params IEnumerable<KeyValuePair<K,V>>[] dicts)
-    {
-        return dicts.Flatten().ToDictionary(kv => kv.Key, kv => kv.Value);
-    }
-
-#pragma warning restore 8714
-
-
     public static void CopyFilesRecursively(String source, String target)
     {
         CopyFilesRecursively(new DirectoryInfo(source), new DirectoryInfo(target));
@@ -210,27 +140,4 @@ public static class Utils
 
 
     public static String ExecutingProcessName => Process.GetCurrentProcess().ProcessName;
-
-    public static IEnumerable<IEnumerable<T>> TraverseWithPath<T>(this T root, Func<T, IEnumerable<T>> getChildren)
-    {
-        var stack = new Stack<IEnumerator<T>>();
-        stack.Push(root.AsSingleEnumerator());
-
-        do
-        {
-            for (var top = stack.Peek(); top.MoveNext(); top = Push(top))
-                yield return stack.Select(p => p.Current);
-
-            var popped = stack.Pop();
-            popped.Dispose();
-        }
-        while (stack.Count > 0);
-
-        IEnumerator<T> Push(IEnumerator<T> node)
-        {
-            var top = getChildren(node.Current).GetEnumerator();
-            stack.Push(top);
-            return top;
-        }
-    }
 }
\ No newline at end of file