1 (defun union-set (set1 set2)
2   (append
3    set1
4    (remove-if
5     (lambda (x)
6       (element-of-set? x set1))
7     set22)))
8 (defun element-of-multiset? (x set)
9   (member x set :test #'equal))
10 (defun intersection-multiset (set1 set2)
11   (cond ((or (null set1) (null set2)) '())
12 	((element-of-multiset? (car set1) set2)
13 	 (cons (car set1)
14 	       (intersection-multiset (cdr set1) set2)))
15 	(t (intersection-multiset (cdr set1) set2))))
16 (defun adjoin-multiset (x set)
17   (cons x set))
18 (defun union-multiset (set1 set2)
19   (append set1 set2))
20 
21 (defun adjoin-set (x set)
22   (cond ((null set) (cons x '()))
23 	((< x (car set)) (cons x set))
24 	((= x (car set)) set)
25 	(t (cons (car set)
26 		 (adjoin-set x (cdr set))))))
27 (defun union-set (set1 set2)
28   (let ((x1 (car set1)) (x2 (car set2)))
29     (cond ((null x1) set2)
30 	  ((null x2) set1)
31 	  ((= x1 x2)
32 	   (cons x1 (union-set (cdr set1) (cdr set2))))
33 	  ((< x1 x2)
34 	   (cons x1 (union-set (cdr set1) set2)))
35 	  (t
36 	   (cons x2 (union-set set1 (cdr set2)))))))