diff --git a/chatmastermind/message.py b/chatmastermind/message.py
index 820d104..3eca26e 100644
--- a/chatmastermind/message.py
+++ b/chatmastermind/message.py
@@ -3,7 +3,7 @@ Module implementing message related functions and classes.
 """
 import pathlib
 import yaml
-from typing import Type, TypeVar, ClassVar, Optional, Any, Union, Final, Literal
+from typing import Type, TypeVar, ClassVar, Optional, Any, Union, Final, Literal, Iterable
 from dataclasses import dataclass, asdict, field
 from .tags import Tag, TagLine, TagError, match_tags
 
@@ -57,6 +57,20 @@ def source_code(text: str, include_delims: bool = False) -> list[str]:
     return code_sections
 
 
+def message_in(message: MessageInst, messages: Iterable[MessageInst]) -> bool:
+    """
+    Searches the given message list for a message with the same file
+    name as the given one (i. e. it compares Message.file_path.name).
+    If the given message has no file_path, False is returned.
+    """
+    if not message.file_path:
+        return False
+    for m in messages:
+        if m.file_path and m.file_path.name == message.file_path.name:
+            return True
+    return False
+
+
 @dataclass(kw_only=True)
 class MessageFilter:
     """
diff --git a/tests/test_message.py b/tests/test_message.py
index 2a9d0ff..0d7953e 100644
--- a/tests/test_message.py
+++ b/tests/test_message.py
@@ -2,7 +2,7 @@ import pathlib
 import tempfile
 from typing import cast
 from .test_main import CmmTestCase
-from chatmastermind.message import source_code, Message, MessageError, Question, Answer, AILine, ModelLine, MessageFilter
+from chatmastermind.message import source_code, Message, MessageError, Question, Answer, AILine, ModelLine, MessageFilter, message_in
 from chatmastermind.tags import Tag, TagLine
 
 
@@ -761,3 +761,17 @@ class MessageFilterTagsTestCase(CmmTestCase):
         self.assertSetEqual(tags_pref, {Tag('atag1')})
         tags_cont = self.message.filter_tags(contain='2')
         self.assertSetEqual(tags_cont, {Tag('btag2')})
+
+
+class MessageInTestCase(CmmTestCase):
+    def setUp(self) -> None:
+        self.message1 = Message(Question('This is a question.'),
+                                tags={Tag('atag1'), Tag('btag2')},
+                                file_path=pathlib.Path('/tmp/foo/bla'))
+        self.message2 = Message(Question('This is a question.'),
+                                tags={Tag('atag1'), Tag('btag2')},
+                                file_path=pathlib.Path('/tmp/bla/foo'))
+
+    def test_message_in(self) -> None:
+        self.assertTrue(message_in(self.message1, [self.message1]))
+        self.assertFalse(message_in(self.message1, [self.message2]))