学步园

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11.1

(define (downup4 wd)

  (se wd

      (bl wd)

      (bl (bl wd))

      (first wd)

      (bl (bl wd))

      (bl wd)

      wd))

11.2

(define (count-ums sent)

  (if(empty? sent)

     0

     (if(equal? 'um (first sent))

     (+ 1(count-ums(bf sent)))

     (count-ums(bf sent)))))

11.3

(define (phone-unspell wd)

  (if(empty? wd)

     '()

     (accumulate word(se (unspell-letter(first wd))

         (phone-unspell (bf wd))))))

11.4

Marilu Henner

11.5

(define (initials sent)

  (if(empty? sent)

     '()

     (se (first(first sent)) (initials (bf sent)))))

11.6

(define (countdown num)

  (if(equal? num 0)

     'BLASTOFF

     (se num (countdown (- num 1)))))

11.7

(define (copies num wd)

  (if(equal? num 0)

     '()

     (se wd (copies (- num 1) wd))))