(defun flat (ls acc)
(print acc)
(cond
   ((null ls) acc)
   ((atom ls) (cons ls acc))
   (t (flat (cdr ls) (flat (car ls) acc)))
))

(defun flat2 (ls)
(cond
   ((null ls) nil)
   ((atom ls) (list ls))
   (t 
      (print (append (flat2 (car ls)) (flat2 (cdr ls))))
      (append (flat2 (car ls)) (flat2 (cdr ls)))
	)
))

(defun help (el)
(cond 
 ((null el) nil)
 ((atom el) (list el))
 (t (help 

(defun flat3 (ls)
mapcar #