Пересечение, разность множеств - Lisp

(defun set-of (lst &optional (r nil))
  (cond ((null lst) r)
        ((atom (car lst)) (if (member (car lst) r) (set-of (cdr lst) r) (set-of (cdr lst) (cons (car lst) r))))
        (t (let ((tlist (set-of (car lst) r)))
             (set-of (cdr lst) tlist)))))
 
(defun inters (s1 s2)
  (cond ((null s1) nil)
        ((member (car s1) s2) (cons (car s1) (inters (cdr s1) s2)))
        (t (inters (cdr s1) s2))))
 
(defun intersect (lst1 lst2)
  (let ((s1 (set-of lst1))
        (s2 (set-of lst2)))
    (inters s1 s2)))
 
==> intersect
 
(intersect '(a s d (h)) '(h a y))
 
==> (h a)
 
(defun sdiff (s1 s2)
  (cond ((null s2) s1)
        ((member (car s2) s1) (sdiff (remove (car s2) s1) (cdr s2)))
        (t (sdiff s1 (cdr s2)))))
 
 
(defun setdiff (lst1 lst2)
  (let ((s1 (set-of lst1))
        (s2 (set-of lst2)))
   (sdiff s1 s2)))
 
==> setdiff
 
(setdiff '(1 2 3 ((3)) 4 ((4 5 6))) '(1 (((3)))))
 
==> (6 5 4 2)