(defun broevi(x)

  (cond
   ((null x) nil )
   ((numberp (car x)) (cons (car x) (broevi (cdr x)) )  )
   ((listp (car x))  (cons (broevi (car x))  (broevi (cdr x) ) )   )
   (T  (broevi (cdr x)))

    )

  )


(broevi '(a (1 2) 4 c))