4 (defn union-set [set1 set2]
7 (cond (empty? set1) set2
9 (= x1 x2) (cons x1 (union-set (rest set1)
11 (< x1 x2) (cons x1 (union-set (rest set1)
13 (> x1 x2) (cons x2 (union-set set1
18 (union-set '() '()) '()
19 (union-set '(1) '()) '(1)
20 (union-set '() '(1)) '(1)
21 (union-set '(1 2 3) '(1 2 3)) '(1 2 3)
22 (union-set '(1 2 3 4) '(1 2 3)) '(1 2 3 4)
23 (union-set '(1 2 4) '(3 4 5)) '(1 2 3 4 5)
24 (union-set '(1 2 3 4) '(5 6 7 8)) '(1 2 3 4 5 6 7 8)
25 (union-set '(1 2 3) '(3 4 5 6)) '(1 2 3 4 5 6)))