9 [(set-member? s (first r)) #f]
10 [else (loop (set-add s (first r)) (rest r))])))
15 (check-equal? (distinct? '()) #t)
16 (check-equal? (distinct? '(1)) #t)
17 (check-equal? (distinct? '(1 2)) #t)
18 (check-equal? (distinct? '(1 1)) #f)
19 (check-equal? (distinct? '(1 2 3)) #t)
20 (check-equal? (distinct? '(1 2 3 3 2)) #f)
21 (check-equal? (distinct? '(a b)) #t)
22 (check-equal? (distinct? '(a b a)) #f)
23 (check-equal? (distinct? '(a b c c)) #f)
24 (check-equal? (distinct? '(1 2 3 4)) #t)
25 (check-equal? (distinct? '(1 2 3 4 5)) #t)
26 (check-equal? (distinct? '(1 (2 3) 4 2 3)) #t))