diff --git a/README_PYPI.md b/README_PYPI.md
index 026c77cf..483fc91c 100644
--- a/README_PYPI.md
+++ b/README_PYPI.md
@@ -175,6 +175,31 @@ entry to whatever pulls it in:
 {'numpy': ['pandas']}
 ```
 
+## Comparing two package lists
+
+`-md` writes a package index. `-diff` compares two:
+
+```console
+$ wppm -diff WinPythonslim-64bit-3.13.5.0.md WinPythonslim-64bit-3.14.7.0.md
+## Changes from WinPythonslim-64bit-3.13.5.0 to WinPythonslim-64bit-3.14.7.0
+
+### Python packages
+
+New packages:
+  * aiofile 3.9.0 (Asynchronous file operations.)
+
+Upgraded packages:
+  * numpy 2.2.6 → 2.5.2 (Fundamental package for array computing in Python)
+
+Removed packages:
+  * astropy 6.1.6 (Astronomy and astrophysics core library)
+```
+
+Any two indexes, in any order: two releases a year apart, or two flavors of the same
+one. No distribution is involved, so two downloaded files are enough. WinPython
+publishes one index per release and flavor, in
+[changelogs/](https://github.com/winpython/winpython/tree/master/changelogs).
+
 ## Environments you have not installed anything into
 
 `-t` points `wppm` at *another* Python distribution, and `-ws` at a plain directory of
diff --git a/wppm/__init__.py b/wppm/__init__.py
index 12e16dd6..b4f744a5 100644
--- a/wppm/__init__.py
+++ b/wppm/__init__.py
@@ -28,6 +28,6 @@
 OTHER DEALINGS IN THE SOFTWARE.
 """
 
-__version__ = '17.12.20260816'
+__version__ = '17.13.20260913'
 __license__ = __doc__
 __project_url__ = 'http://winpython.github.io/'
diff --git a/wppm/wppm.py b/wppm/wppm.py
index 58569357..b0590957 100644
--- a/wppm/wppm.py
+++ b/wppm/wppm.py
@@ -81,8 +81,8 @@ def render_markdown_for_list(self, title, items):
         return md
     
     def get_package_index_data(self, python_executable_directory: str|None = None, winpyver2: str|None = None,
-                                         flavor: str|None = None, architecture_bits: int|None = None
-                                         , release_level: str|None = None, wheeldir: str|None = None) -> dict:
+                                         flavor: str|None = None, release_level: str|None = None,
+                                         wheeldir: str|None = None) -> dict:
         """Collects the package index data: distribution identity, tools, packages, wheelhouse."""
         my_ver , my_arch = utils.get_python_infos(python_executable_directory or self.target)
         my_winpyver2 = winpyver2 or os.getenv("WINPYVER2","")
@@ -114,10 +114,10 @@ def get_package_index_data(self, python_executable_directory: str|None = None, w
         }
 
     def generate_package_index_markdown(self, python_executable_directory: str|None = None, winpyver2: str|None = None,
-                                         flavor: str|None = None, architecture_bits: int|None = None
-                                         , release_level: str|None = None, wheeldir: str|None = None) -> str:
+                                         flavor: str|None = None, release_level: str|None = None,
+                                         wheeldir: str|None = None) -> str:
         """Generates a Markdown formatted package index page."""
-        data = self.get_package_index_data(python_executable_directory, winpyver2, flavor, architecture_bits, release_level, wheeldir)
+        data = self.get_package_index_data(python_executable_directory, winpyver2, flavor, release_level, wheeldir)
         d = data["distribution"]
         as_tuples = lambda items: [(i["name"], i["url"], i["version"], i["summary"]) for i in items]