Создать список, состоящий из элементов исходного списка, только тех, которые являются списком

(defun func-list(List)
  (cond ((atom (car List)) (func-list(cdr List)))
        ((listp (car List)) (list (car List) (func-list(cdr List))))
  )
)

(func-list '((a b) e f () (c d)))

(defun lists (w)
  (cond ((null w) nil)
        ((listp (car w)) (cons (car w) (lists (cdr w))))
        (t (lists (cdr w)))))
 
> (lists '((a b) e f () (c d)))
((A B) NIL (C D))

(defun lists (w)
  (when w (if (listp (car w))
              (cons (car w) (lists (cdr w)))
              (lists (cdr w)))))
 
> (lists '((a b) e f () (c d)))
((A B) NIL (C D))

(defun lists (w &aux (a (car w)) (d (cdr w)))
  (when w (if (listp a) (cons a (lists d))
              (lists d))))
 
> (lists '((a b) e f () (c d)))
((A B) NIL (C D))

(defun lists (w)
  (loop for a in w 
        when (listp a) collect a))
 
> (lists '((a b) e f () (c d)))
((A B) NIL (C D))

(defun lists (w)
  (remove-if-not #'listp w))
 
> (lists '((a b) e f () (c d)))
((A B) NIL (C D))

(defun lists (w &optional ac
              &aux  (a (car w)) (d (cdr w)))
  (if w (lists d (if (listp a) (cons a ac) ac))
      (nreverse ac)))
 
> (lists '((a b) e f () (c d)))
((A B) NIL (C D))

(defun func-list(List)
  (cond ((null list) nil)
           ((atom (car List)) (func-list (cdr List)))
           ((listp (car List)) (cons (car List) (func-list (cdr List))))))
 
==> FUNC-LIST
 
(func-list '(1 2 (a b) c d (e f)))
 
==> ((A B) (E F))

(defun task (list)
  (remove-if 'atom list))
 
==> TASK
 
(task '(1 2 (a b) c d (e f)))
 
==> ((A B) (E F))

(defun lists (w &optional ac &aux  (a (car w)))
  (if w (lists (cdr w) (if (listp a) (cons a ac)
                           ac))
      (nreverse ac)))
 
> (lists '((a b) e f () (c d)))
((A B) NIL (C D))

(defparameter *w* '((a b) e f () (c d)))
 
(defun lists (w)
  (remove-if-not #'listp w))
 
> (lists *w*)
((A B) NIL (C D))
> *w*
((A B) E F NIL (C D))