[이영석]

(is-prefix-free-list? '((0) (1 0) (1 1 1) (1 1 0))) ;t
(is-prefix-free-list? '((1) (0 1) (0 0 1) (0 1 1))) ;f
(is-prefix-free-list? '((0 0 0 0) (0 0 0 1) (0 0 1 1) (1 1 0 1) (1 0 0 0))) ;t
(is-prefix-free-list? '((0 0 0) (0 0 1) (0 1 0) (0 1 1) (1 0 0) (1 1 1))) ;t
(is-prefix-free-list? '((0 0 0) (0 0 1) (0 1 0) (0 1 1) (1 0 0) (1 1 1) (0 0 0 1))) ;f

[현.철]

(define t1 (make-table))
(define t2 (add-table "a" 1 t1))
(define t3 (add-table "b" 2 t2))
(define t4 (add-table "c" 3 t3))
(define t5 (add-table "d" 4 t4))
(define t6 (remove-table "b" t5))
;(define t7 (remove-table "b" t6)) ;error
;(define t8 (find-table "b" t6)) ;error
(define t9 (add-table "a" 5 t6))

(define t10 (map-table (lambda (key val) (cons key (- 6 val))) t9))
(define t11 (fold-table (lambda (key val result) (+ result (cdr val))) 0 t10))

t5 ;(("d" . 4) ("c" . 3) ("b" . 2) ("a" . 1))
t6 ;(("d" . 4) ("c" . 3) ("a" . 1))
t9 ;(("a" . 5) ("d" . 4) ("c" . 3))
t10 ;(("a" "a" . 1) ("d" "d" . 2) ("c" "c" . 3))
t11 ;6

기본문제 테스트셋입니다.
t7과 t8은 에러가 나야 합니다.
t5~t10의 원소순서는 상관없다고 하시네요