;; Computing a list structure can be a costly operation on huge lists
;; (a few thousand lines long). Thus, code should follow the rule :
-;; "collect once, use many". As a corollary, it is usally a bad idea
+;; "collect once, use many". As a corollary, it is usually a bad idea
;; to use directly an interactive function inside the code, as those,
;; being independent entities, read the whole list structure another
;; time.