this should do; will it finish in time?

p21/p21.org

@@ -165,13 +165,29 @@ So we start from all possible combinations of keypad pairs
    (--map (cons it (connecting-paths (char-pairs-to-coordinate-pairs it dir-keypad-data) dir-keypad-data)) direction-pairs)
    first-step (--map (cons (car it) (pick-shortest-string (cdr it))) basis-induction) )
 
+  ; here first-step contains the keys that need to be pressed on the
+  ; human keypad to have the first keypad do as described
   (defun iterate-robot (s al)
     (apply #'concat (--map (cdr (assoc it al)) (split-into-char-pairs (concat "A" s)))))
 
   (defun iterate-step (l)
    (--map (cons (car it) (pick-shortest-string
             (--map (iterate-robot it l) (cdr it))))
-  	basis-induction)
-   )
+    basis-induction))
 
+  ; here iterate-step takes a list at step n and returns the same list
+  ; at step n+1
+  (setq last-step (funcall (-iteratefn 'iterate-step 24) first-step))
+
+  (defun shortest-stuff (s)
+    (length (apply 'concat (--map (pick-shortest-string (--map (iterate-robot it last-step) it))
+                                  (directions-for-string s numeric-keypad-data)))))
+
+  (defun complexity (s)
+      (* (string-to-number (replace-in-string "A" "" s))
+       (shortest-stuff s)))
+
+    (-reduce #'+ (-map #'complexity data))
+
+  ;oh, it does…
 #+end_src