2.18
(define (reverse items) (if (null? (cdr items)) items (append (reverse (cdr items)) (list(car items))) ) ) (reverse (list 1 2 3 4))
2.17
(define (list-pair items) (if (null? (cdr items)) items (list-pair (cdr items)) ) ) (list-pair (list 1 2 3 4))