(defun in (elem array)
	(cond
		((null array) nil)
		((eql elem (car array)) t)
		(t (in elem (cdr array)))
	)
)

(defun set (array)
	(cond
		((null array) nil)
		((in (car array) (cdr array)) (set (cdr array)))
		(t (cons (car array) (set (cdr array))))
	)
)

(defun union (set1 set2)
	(cond
		((null set1) set2)
		((null set2) set1)
		((in (car set2) set1) (union set1 (cdr set2)))
		(t (union (cons (car set2) set1) (cdr set2)))
	)
)

(print (union '(1 2 3 4) '(6 3 4 5)))