Some terse "context-free" Emacs Lisp snippets that hopefully speak for
themselves.

* The prefix argument
#+begin_src elisp
(defun my/prefix-arg-demo (arg)
  (interactive (list current-prefix-arg))
  (insert
   (let ((num (prefix-numeric-value arg)))
    (format "%s	%d	%s\n"
           arg
           num
           (cond ((null arg)     "N/A")
                 ((numberp arg)  (format "M-%d or C-u %d" arg arg))
                 ((equal arg '-) (format "M-- or C-u -"))
                 ((listp arg)
                  (if (< num 0)
                      (format "(M-- or C-u -) C-u × %d" (log (- num) 4))
                    (format "C-u × %d" (log num 4)))))))))
#+end_src
#+begin_example
nil	1	N/A
2	2	M-2 or C-u 2
-	-1	M-- or C-u -
(-16)	-16	(M-- or C-u -) C-u × 2
(64)	64	C-u × 3
#+end_example