(defun traverse-largeur (l)
  (TL (list l) '())
  )


(defun TL (file result)
  (if file
    (TL (append (rest file) 
                (if (atom (first file)) '() (first file)))

        (append result (list (first file)))
        )
    result

    ))
  


;; (traverse-largeur '()) -> (NIL)
;; (traverse-largeur '(1 2 3))  -> ((1 2 3) 1 2 3)

;; (traverse-largeur '(1 (2 3) 4)) -> ((1 (2 3) 4) 1 (2 3) 4 2 3)


(defun subst0 (dans avant apres)
  
  (cond
   ((equal dans avant) apres)
   ((atom dans) dans)
   
   (t (cons (subst0 (first dans) avant apres)
            (subst0 (rest dans) avant apres))
      )
   
   
   )
  )

;; (time (subst0 '(1 2 3 4 2) 2 'a))
;; (time (subst0 '(1 (2 3 (6 7 2) 4) 2) 2 'a))
;; (time (subst0 '(1 (3 5 (6 () (7 8)) 9) 2) 2 'a)) -> 96 cons

(defun subst1 (dans avant apres)
  (flet ((ecocons (x y) 
           (if (and (eq x (first dans))
                    (eq y (rest dans)))
             dans
             (cons x y))
           )
         )
    (cond
     ((equal dans avant) apres)
     ((atom dans) dans)

     (t (ecocons (subst1 (first dans) avant apres)
                 (subst1 (rest dans) avant apres))
        )

     )
    )
  )


;; (time (subst1 '(1 2 3 4 2) 2 'a))
;; (time (subst1 '(1 (2 3 (6 7 2) 4) 2) 2 'a))
;; (time (subst1 '(1 (3 5 (6 () (7 8)) 9) 2) 2 'a)) -> 24 cons


(defun subst3 (dans avant apres)
    
    (cond
     ((equal dans avant) apres)
     ((atom dans) dans)
     (t (let ((s1 (subst3 (first dans) avant apres))
              (s2 (subst3 (rest dans) avant apres))
              )
          (if  (and (eq (first dans) s1) (eq (rest dans) s2))
            dans
            (cons s1 s2))))

     )
    )
  

;; (time (subst3 '(1 2 3 4 2) 2 'a))
;; (time (subst3 '(1 (2 3 (6 7 2) 4) 2) 2 'a))
;; (time (subst3 '(1 (3 5 (6 () (7 8)) 9) 2) 2 'a)) -> 24 cons