3 (require "ch2_3_3.rkt")
5 (define (union-set set1 set2)
6 (cond ((null? set1) set2)
8 ((element-of-set? (car set1) set2) (union-set (cdr set1) set2))
9 (else (cons (car set1) (union-set (cdr set1) set2)))))
11 (union-set '(1 2 3 4) '(5 6 7 8))
12 (union-set '(1 2 3 4) '(1 2 3 4))
13 (union-set '(1 2 3 4) '(1 2 7 8))