Do not install python' and reduce package-selected-packages' setup

README.org

@@ -267,8 +267,6 @@ The [[info:emacs#Init File][init file (info)]] does not load the ~custom-file~ a
                  (hyperbole . "gnu-devel")
                  (marginalia . "gnu-devel")
                  (org . "gnu-devel")
-                 ,(when (version< emacs-version "28.9.9")
-                    '(python . "gnu-devel"))
                  (queue . "gnu")
                  (rainbow-mode . "gnu")
                  (spinner . "gnu")
@@ -283,14 +281,10 @@ The [[info:emacs#Init File][init file (info)]] does not load the ~custom-file~ a
 (custom-set-variables
  '(package-selected-packages
    `,(delq nil `(async              ; asynchroneous processing
-                 auctex             ; Aalborg University Center TeX
                  debbugs            ; access the GNU bug tracker
                  no-littering       ; keep `user-emacs-directory' clean
                  org                ; thought organizer
-                 ,(when (version< emacs-version "28.9.9")
-                    'python)        ; major mode to edit Python files
-                 wgrep              ; open a writable grep buffer
-                 xr))))             ; undo rx to grok regular expressions
+                 wgrep))))          ; open a writable grep buffer
 #+end_src
 
 #+caption[Customize the fourth set of Emacs variables]:
@@ -1645,6 +1639,22 @@ suggestions on those pages.
      '(xref-search-program 'ugrep))))
 #+end_src
 
+** [[https://github.com/mattiase/xr#readme][XR - Emacs regexp parser and analyzer]]
+:PROPERTIES:
+:CUSTOM_ID: sec:ensure-xr-installation
+:END:
+
+[[https://github.com/mattiase/xr#readme][XR]] converts Emacs regular expressions to the structured =rx= form, thus being an
+inverse of =rx=. It can also find mistakes and questionable constructs inside
+regexp strings.
+
+#+caption[Ensure =xr= installation]:
+#+caption: Ensure =xr= installation.
+#+name: lst:ensure-xr-installation
+#+begin_src emacs-lisp
+(when (ensure-package-installation 'xr))
+#+end_src
+
 * [[info:emacs#Version Control][Version Control (info)]]
 :PROPERTIES:
 :CUSTOM_ID: sec:version-control
@@ -1849,8 +1859,8 @@ elisp library file has no autoload cookie.  Without prior loading of =tex.el=,
 Emacs will complain that ~TeX-master~ is no safe local variable in case it reads
 a LaTeX file that sets ~TeX-master~.  The list below summarizes the main [[https://en.wikipedia.org/wiki/AUCTeX][AUCTeX]]
 configuration objectives:
-1. Listing [[lst:require-tex]] initializes [[https://en.wikipedia.org/wiki/AUCTeX][AUCTeX]] properly for =LuaTeX= or
- =LuaLaTeX=.
+1. Listing [[lst:require-tex]] ensures installation of [[https://en.wikipedia.org/wiki/AUCTeX][AUCTeX]] and initializes [[https://en.wikipedia.org/wiki/AUCTeX][AUCTeX]]
+   properly for =LuaTeX= or =LuaLaTeX=.
 2. Listing [[lst:require-tex]] also enables [[https://git.savannah.gnu.org/cgit/auctex.git/patch/?id=f464242eab092e610dda6b654e6fd197ef649d3eAA][indenting between square brackets]]
    which is a recent feature.
 3. Listing [[lst:update-lualatex-opentype-font-name-database]] defines a function to
@@ -1866,6 +1876,7 @@ configuration objectives:
 #+caption: Require and configure =TeX=.
 #+name: lst:require-tex
 #+begin_src emacs-lisp
+(when (ensure-package-installation 'auctex)
   ;; Use `require' to make `TeX-master' a safe local variable.
   (when (require 'tex nil 'noerror)
     (custom-set-variables
@@ -1876,7 +1887,7 @@ configuration objectives:
      '(TeX-install-font-lock #'font-latex-setup)
      '(TeX-parse-self t)
      ;; Disable `TeX-electric-math' to prevent collisions with `smartparens'.
-   '(TeX-electric-math nil)))
+     '(TeX-electric-math nil))))
 #+end_src
 
 #+caption[Update the =LuaLaTeX OpenType Font=  name database]: