diff --git a/.github/workflows/github-action-test-js.yml b/.github/workflows/github-action-test-js.yml
index dd83a9df..c368a083 100644
--- a/.github/workflows/github-action-test-js.yml
+++ b/.github/workflows/github-action-test-js.yml
@@ -17,9 +17,9 @@ jobs:
         node-version: [14.x, 16.x, 18.x, 20.x]
 
     steps:
-    - uses: actions/checkout@v2
+    - uses: actions/checkout@v4
     - name: Use Node.js ${{ matrix.node-version }}
-      uses: actions/setup-node@v2
+      uses: actions/setup-node@v4
       with:
         node-version: ${{ matrix.node-version }}
         cache: 'npm'
diff --git a/.github/workflows/github-action-test-python.yml b/.github/workflows/github-action-test-python.yml
index 2d3f963b..db70dcc9 100644
--- a/.github/workflows/github-action-test-python.yml
+++ b/.github/workflows/github-action-test-python.yml
@@ -14,9 +14,9 @@ jobs:
         # You need to change to branch protection rules if you change the versions here
         python-version: [3.12.1, 3.13.0]
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v4
       - name: Set up Python ${{ matrix.python-version }}
-        uses: actions/setup-python@v2
+        uses: actions/setup-python@v5
         with:
           python-version: ${{ matrix.python-version }}
       - name: Test
diff --git a/python/deps/untypy/test/impl/test_simple.py b/python/deps/untypy/test/impl/test_simple.py
index 06cf04e4..6e70e37d 100644
--- a/python/deps/untypy/test/impl/test_simple.py
+++ b/python/deps/untypy/test/impl/test_simple.py
@@ -59,6 +59,7 @@ def test_attributes(self):
         def m(x: A) -> None:
             self.assertEqual(x.foo, 42)
             x.foo = 43
+            self.assertEqual(x.foo, 43)
 
         m(a)
         self.assertEqual(a.foo, 43)
diff --git a/python/deps/untypy/test/util_test/test_wrapper.py b/python/deps/untypy/test/util_test/test_wrapper.py
index 04cc6edf..9d3d921d 100644
--- a/python/deps/untypy/test/util_test/test_wrapper.py
+++ b/python/deps/untypy/test/util_test/test_wrapper.py
@@ -77,12 +77,13 @@ def _test_api_complete(self, obj, ignore=[]):
                      '__weakref__', '__wrapped__', '_DictWrapper__marker', '__setstate__',
                      '__getstate__', '__firstlineno__', '__static_attributes__'
                      ] + ignore
-        for x in dir(wrapped):
-            if x in blacklist: continue
-            m = getattr(wrapped, x)
-            if not hasattr(m, '__module__'):
-                self.fail(f'Attribute {x} not defined')
-            elif m.__module__ != expectedModule:
+        for x in dir(obj):
+            if x in blacklist:
+                continue
+            a = getattr(wrapped, x)
+            if not hasattr(a, '__module__'):
+                self.fail(f'Attribute {x} not defined. obj={obj}, a={a}, wrapped={wrapped}')
+            elif a.__module__ != expectedModule:
                 self.fail(f'Attrribute {x} not defined in {expectedModule}')
 
     def test_list_api_complete(self):
diff --git a/python/deps/untypy/untypy/util/wrapper.py b/python/deps/untypy/untypy/util/wrapper.py
index 8d4eaa79..1ffe3eae 100644
--- a/python/deps/untypy/untypy/util/wrapper.py
+++ b/python/deps/untypy/untypy/util/wrapper.py
@@ -1,44 +1,11 @@
 import typing
-import abc
 import collections
-from untypy.error import UntypyError
 from untypy.util.debug import debug
 
 def _f():
     yield 0
 generatorType = type(_f())
 
-class WyppWrapError(Exception):
-    pass
-
-def _readonly(self, *args, **kwargs):
-    raise RuntimeError("Cannot modify ReadOnlyDict")
-
-class ReadOnlyDict(dict):
-    __setitem__ = _readonly
-    __delitem__ = _readonly
-    pop = _readonly
-    popitem = _readonly
-    clear = _readonly
-    update = _readonly
-    setdefault = _readonly
-
-def patch(self, ty, extra):
-    # SW (2024-10-18): With python 3.13 there is the behavior that extra is modified after patching
-    # the object. I never found out who is doing the modification. By wrapping extra with
-    # ReadOnlyDict, everything works. Strangely, no error occurs somewhere.
-    self.__extra__ = ReadOnlyDict(extra)
-    w = self.__wrapped__
-    m = None
-    if hasattr(w, '__module__'):
-        m = getattr(w, '__module__')
-    ty.__module__ = m
-    try:
-        self.__class__ = ty
-    except TypeError as e:
-        raise WyppWrapError(f'Cannot wrap {self.__wrapped__} of type {type(self.__wrapped__)} ' \
-            f'at type {ty}. Original error: {e}')
-
 class WrapperBase:
     def __eq__(self, other):
         if hasattr(other, '__wrapped__'):
@@ -49,17 +16,7 @@ def __ne__(self, other):
         return not self.__eq__(other)
     def __hash__(self):
         return hash(self.__wrapped__)
-    def __patch__(self, ms, name=None, extra=None):
-        if extra is None:
-            extra = {}
-        cls = self.__class__
-        if name is None:
-            name = cls.__name__
-        ty = type(name, (cls,), ms)
-        patch(self, ty, extra)
     def __repr__(self):
-        #w = self.__wrapped__
-        #return f"Wrapper(addr=0x{id(self):09x}, wrapped_addr=0x{id(w):09x}, wrapped={repr(w)}"
         return repr(self.__wrapped__)
     def __str__(self):
         return str(self.__wrapped__)
@@ -72,27 +29,6 @@ def __reduce__(self): return self.__wrapped__.__reduce__()
     def __reduce_ex__(self): return self.__wrapped__.__reduce_ex__()
     def __sizeof__(self): return self.__wrapped__.__sizeof__()
 
-class ObjectWrapper(WrapperBase):
-    def __init__(self, baseObject):
-        self.__dict__ = baseObject.__dict__
-        self.__wrapped__ = baseObject
-    def __patch__(self, ms, name=None, extra=None):
-        if extra is None:
-            extra = {}
-        cls = self.__class__
-        if name is None:
-            name = cls.__name__
-        wrappedCls = type(self.__wrapped__)
-        ty = type(name, (wrappedCls, cls), ms)
-        patch(self, ty, extra)
-
-class ABCObjectWrapper(abc.ABC, ObjectWrapper):
-    pass
-
-# Superclasses in reverse order.
-class ABCObjectWrapperRev(ObjectWrapper, abc.ABC):
-    pass
-
 # A wrapper for list such that the class is a subclass of the builtin list class.
 class ListWrapper(WrapperBase, list): # important: inherit from WrapperBase first
     def __new__(cls, content):
@@ -224,33 +160,10 @@ def __new__(cls, content):
         self.__wrapped__ = content
         return self
 
-# These methods are not delegated to the wrapped object
-_blacklist = [
-    '__class__', '__delattr__', '__dict__', '__dir__', '__doc__',
-    '__getattribute__', '__get_attr_', '__init_subclass__'
-    '__init__', '__new__', '__del__', '__repr__', '__setattr__', '__str__',
-    '__hash__', '__eq__', '__patch__',
-    '__class_getitem__',  '__subclasshook__',
-    '__firstlineno__', '__static_attributes__']
-
-_extra = ['__next__']
-
 # SimpleWrapper is a fallback for types that cannot be used as base types
 class SimpleWrapper(WrapperBase):
-    def __init__(self, baseObject):
-        self.__wrapped__ = baseObject
-    def __patch__(self, ms, name=None, extra=None):
-        if extra is None:
-            extra = {}
-        cls = self.__class__
-        if name is None:
-            name = cls.__name__
-        baseObject = self.__wrapped__
-        for x in dir(baseObject) + _extra:
-            if x not in ms and x not in _blacklist and hasattr(baseObject, x):
-                ms[x] = getattr(baseObject, x)
-        ty = type(name, (cls,), ms) #
-        patch(self, ty, extra)
+    def __init__(self, wrapped):
+        self.__wrapped__ = wrapped
 
 class ValuesViewWrapper(SimpleWrapper):
     pass
@@ -264,46 +177,99 @@ class KeysViewWrapper(SimpleWrapper):
     pass
 collections.abc.KeysView.register(KeysViewWrapper)
 
+def _wrap(wrapped, methods, mod, name, extra, cls):
+    if extra is None:
+        extra = {}
+    # Dynamically create a new class:
+    # type(class_name, base_classes, class_dict)
+    WrapperClass = type(
+        name,
+        (cls,),
+        methods
+    )
+    WrapperClass.__module__ = mod
+    w = WrapperClass(wrapped)
+    w.__extra__ = extra
+    return w
+
+def wrapSimple(wrapped, methods, name, extra, cls=SimpleWrapper):
+    if name is None:
+        name = cls.__name__
+        mod = None
+    else:
+        if hasattr(wrapped, '__module__'):
+            mod = wrapped.__module__
+        else:
+            mod = None
+    for x in ['__next__', '__iter__']:
+        if x not in methods and hasattr(wrapped, x):
+            attr = getattr(wrapped, x)
+            methods[x] = attr
+    return _wrap(wrapped, methods, mod, name, extra, cls)
+
+def wrapObj(wrapped, methods, name, extra):
+    class BaseWrapper(WrapperBase, wrapped.__class__):
+        def __init__(self, wrapped):
+            self.__dict__ = wrapped.__dict__
+            self.__wrapped__ = wrapped
+    if name is None:
+        name = 'ObjectWrapper'
+    if hasattr(wrapped, '__module__'):
+        mod = getattr(wrapped, '__module__')
+    else:
+        mod = None
+    return _wrap(wrapped, methods, mod, name, extra, BaseWrapper)
+
+def wrapBuiltin(wrapped, methods, name, extra, cls):
+    if name is None:
+        name = cls.__name__
+    return _wrap(wrapped, methods, None, name, extra, cls)
+
 def wrap(obj, methods, name=None, extra=None, simple=False):
     if extra is None:
         extra = {}
+    wrapper = None
     if simple:
-        w = SimpleWrapper(obj)
+        w = wrapSimple(obj, methods, name, extra)
+        wrapper = 'SimpleWrapper'
     elif isinstance(obj, list):
-        w = ListWrapper(obj)
+        w = wrapBuiltin(obj, methods, name, extra, ListWrapper)
+        wrapper = 'ListWrapper'
     elif isinstance(obj, tuple):
-        w = TupleWrapper(obj)
+        w = wrapBuiltin(obj, methods, name, extra, TupleWrapper)
+        wrapper = 'TupleWrapper'
     elif isinstance(obj, dict):
-        w = DictWrapper(obj)
+        w = wrapBuiltin(obj, methods, name, extra, DictWrapper)
+        wrapper = 'DictWrapper'
     elif isinstance(obj, str):
-        w = StringWrapper(obj)
+        w = wrapBuiltin(obj, methods, name, extra, StringWrapper)
+        wrapper = 'StringWrapper'
     elif isinstance(obj, set):
-        w = SetWrapper(obj)
+        w = wrapBuiltin(obj, methods, name, extra, SetWrapper)
+        wrapper = 'SetWrapper'
     elif isinstance(obj, collections.abc.ValuesView):
-        w = ValuesViewWrapper(obj)
+        w = wrapSimple(obj, methods, name, extra, ValuesViewWrapper)
+        wrapper = 'ValuesViewWrapper'
     elif isinstance(obj, collections.abc.KeysView):
-        w = KeysViewWrapper(obj)
+        w = wrapSimple(obj, methods, name, extra, KeysViewWrapper)
+        wrapper = 'KeysViewWrapper'
     elif isinstance(obj, collections.abc.ItemsView):
-        w = ItemsViewWrapper(obj)
+        w = wrapSimple(obj, methods, name, extra, ItemsViewWrapper)
+        wrapper = 'ItemsViewWrapper'
     elif isinstance(obj, typing.Generic):
-        w = SimpleWrapper(obj)
+        w = wrapSimple(obj, methods, name, extra)
+        wrapper = 'SimpleWrapper'
     elif isinstance(obj, generatorType):
-        w = SimpleWrapper(obj)
-    elif isinstance(obj, abc.ABC) and hasattr(obj, '__dict__'):
-        try:
-            w = ABCObjectWrapper(obj)
-        except WyppWrapError:
-            try:
-                w = ABCObjectWrapperRev(obj)
-            except WyppWrapError:
-                w = SimpleWrapper(obj)
+        w = wrapSimple(obj, methods, name, extra)
+        wrapper = 'SimpleWrapper'
     elif hasattr(obj, '__dict__'):
-        w = ObjectWrapper(obj)
+        w = wrapObj(obj, methods, name, extra)
+        wrapper = 'ObjectWrapper'
     else:
-        w = SimpleWrapper(obj)
-    w.__patch__(methods, name, extra)
+        w = wrapSimple(obj, methods, name, extra)
+        wrapper = 'SimpleWrapper'
     wname = name
     if wname is None:
         wname = str(type(w))
-    debug(f"Wrapping {obj} at 0x{id(obj):09x} as {wname}, simple={simple}, wrapper=0x{id(w):09x}")
+    debug(f"Wrapping {obj} at 0x{id(obj):09x} as {wname}, simple={simple}, wrapper=0x{id(w):09x} ({wrapper})")
     return w
diff --git a/python/fileTests b/python/fileTests
index c88d21de..807f8523 100755
--- a/python/fileTests
+++ b/python/fileTests
@@ -289,6 +289,8 @@ checkWithOutputAux yes 0 test-data/testForwardTypeInRecord.py
 checkWithOutputAux yes 0 test-data/testForwardTypeInRecord2.py
 checkWithOutputAux yes 0 test-data/testUnionOfUnion.py
 checkWithOutputAux yes 1 test-data/testRecordTypes.py
+checkWithOutputAux yes 0 test-data/testDisappearingObject_01.py
+checkWithOutputAux yes 0 test-data/testDisappearingObject_02.py
 
 function is_min_version()
 {
diff --git a/python/run b/python/run
index 6eb6a50f..e61be5c5 100755
--- a/python/run
+++ b/python/run
@@ -1,10 +1,11 @@
 #!/bin/bash
 
+PY=python3.13 
 SCRIPT_DIR="$( cd "$( dirname "${BASH_SOURCE[0]}" )" &> /dev/null && pwd )"
 
 OPTS="--quiet"
 # OPTS="--verbose"
 
-PYTHONPATH="$SCRIPT_DIR"/site-lib:"$PYTHONPATH" python3 "$SCRIPT_DIR"/src/runYourProgram.py \
+PYTHONPATH="$SCRIPT_DIR"/site-lib:"$PYTHONPATH" $PY "$SCRIPT_DIR"/src/runYourProgram.py \
     --no-clear $OPTS "$@"
 exit $?
diff --git a/python/test-data/testDisappearingObject_01.err b/python/test-data/testDisappearingObject_01.err
new file mode 100644
index 00000000..e69de29b
diff --git a/python/test-data/testDisappearingObject_01.out b/python/test-data/testDisappearingObject_01.out
new file mode 100644
index 00000000..3252461b
--- /dev/null
+++ b/python/test-data/testDisappearingObject_01.out
@@ -0,0 +1,2 @@
+['subdir']
+Directory('stefan')
diff --git a/python/test-data/testDisappearingObject_01.py b/python/test-data/testDisappearingObject_01.py
new file mode 100644
index 00000000..aabc05fa
--- /dev/null
+++ b/python/test-data/testDisappearingObject_01.py
@@ -0,0 +1,77 @@
+# This test comes from a bug reported by a student, 2025-05-8
+from __future__ import annotations
+from wypp import *
+import gc
+
+class FileSystemEntry:
+    def __init__(self, name: str):
+        self.name = name
+    def getName(self) -> str:
+        return self.name
+    def getContent(self) -> str:
+        raise Exception('No content')
+    def getChildren(self) -> list[FileSystemEntry]:
+        return []
+    def findChild(self, name: str) -> FileSystemEntry:
+        for c in self.getChildren():
+            if c.getName() == name:
+                return c
+        raise Exception('No child with name ' + name)
+    def addChild(self, child: FileSystemEntry) -> None:
+        raise Exception('Cannot add child to ' + repr(self))
+
+class Directory(FileSystemEntry):
+    def __init__(self, name: str, children: list[FileSystemEntry] = []):
+        super().__init__(name)
+        self.__children = children
+    def getChildren(self) -> list[FileSystemEntry]:
+        return self.__children
+    def addChild(self, child: FileSystemEntry):
+        self.__children.append(child)
+    def __repr__(self):
+        return 'Directory(' + repr(self.getName()) + ')'
+
+class File:
+    def __init__(self, name: str, content: str):
+        raise ValueError()
+        super().__init__(name)
+        self.content = content
+    def getContent(self) -> str:
+        return self.content
+
+class Link(FileSystemEntry):
+    def __init__(self, name: str, linkTarget: FileSystemEntry):
+        super().__init__(name)
+        self.__linkTarget = linkTarget
+    def getChildren(self) -> list[FileSystemEntry]:
+        return self.__linkTarget.getChildren()
+    def getContent(self) -> str:
+        return self.__linkTarget.getContent()
+    def addChild(self, child: FileSystemEntry):
+        self.__linkTarget.addChild(child)
+    def __repr__(self):
+        return ('Link(' + repr(self.getName()) + ' -> ' +
+                repr(self.__linkTarget) + ')')
+    def getLinkTarget(self) -> FileSystemEntry:
+        return self.__linkTarget
+
+class CryptoFile:
+    def __init__(self, name: str, content: str):
+        raise ValueError()
+        super().__init__(name)
+        self.content = content
+    def getContent(self) -> str:
+        return 'CRYPTO_' + 'X'*len(self.content)
+    def __repr__(self):
+        return 'CryptoFile(' + repr(self.getName())
+
+def test_link():
+    stefan  = Directory('stefan', [])
+    wehr    = Link('wehr', stefan)
+    l1 = [x.getName() for x in wehr.getChildren()]
+    wehr.addChild(Directory('subdir', []))
+    l2 = [x.getName() for x in wehr.getChildren()]
+    print(l2)
+    print(stefan)
+
+test_link()
diff --git a/python/test-data/testDisappearingObject_02.err b/python/test-data/testDisappearingObject_02.err
new file mode 100644
index 00000000..e69de29b
diff --git a/python/test-data/testDisappearingObject_02.out b/python/test-data/testDisappearingObject_02.out
new file mode 100644
index 00000000..e69de29b
diff --git a/python/test-data/testDisappearingObject_02.py b/python/test-data/testDisappearingObject_02.py
new file mode 100644
index 00000000..97d8daca
--- /dev/null
+++ b/python/test-data/testDisappearingObject_02.py
@@ -0,0 +1,68 @@
+# This test comes from a bug reported by a student, 2025-05-8
+from __future__ import annotations
+from wypp import *
+from abc import ABC, abstractmethod
+
+class FileSystemEntry(ABC):
+    def __init__(self, name: str):
+        self.__name = name
+    def getName(self) -> str:
+        return self.__name
+    def getContent(self) -> str:
+        raise Exception('No content')
+    def getChildren(self) -> list[FileSystemEntry]:
+        return []
+    def findChild(self, name: str) -> FileSystemEntry:
+        for c in self.getChildren():
+            if c.getName() == name:
+                return c
+        raise Exception('No child with name ' + name)
+    def addChild(self, child: FileSystemEntry) -> None:
+        raise Exception('Cannot add child to ' + repr(self))
+
+class Directory(FileSystemEntry):
+    def __init__(self, name: str, children: list[FileSystemEntry] = []):
+        super().__init__(name)
+        self.__children = children[:]
+    def getChildren(self) -> list[FileSystemEntry]:
+        return self.__children[:]
+    def addChild(self, child: FileSystemEntry):
+        self.__children.append(child)
+    def __repr__(self):
+        return 'Directory(' + repr(self.getName()) + ')'
+
+class File(FileSystemEntry):
+    def __init__(self, name: str, content: str):
+        super().__init__(name)
+        self.__content = content
+    def getContent(self) -> str:
+        return self.__content
+    def __repr__(self):
+        return 'File(' + repr(self.getName()) + ')'
+
+class Link(FileSystemEntry):
+    def __init__(self, name: str, linkTarget: FileSystemEntry):
+        super().__init__(name)
+        self.__linkTarget = linkTarget
+    def getChildren(self) -> list[FileSystemEntry]:
+        return self.__linkTarget.getChildren()
+    def getContent(self) -> str:
+        return self.__linkTarget.getContent()
+    def addChild(self, child: FileSystemEntry):
+        self.__linkTarget.addChild(child)
+    def __repr__(self):
+        return ('Link(' + repr(self.getName()) + ' -> ' +
+                repr(self.__linkTarget) + ')')
+    def getLinkTarget(self) -> FileSystemEntry:
+        return self.__linkTarget
+
+def test_link():
+    stefan  = Directory('stefan', [File('notes.txt', 'Notiz')])
+    wehr    = Link('wehr', stefan)
+    l1 = [x.getName() for x in wehr.getChildren()]
+    wehr.addChild(Directory('subdir', []))
+    l2 = [x.getName() for x in stefan.getChildren()]
+    l3 = [x.getName() for x in wehr.getChildren()]
+
+
+test_link()