[racket-users] Transfer code from "intermediate student with lamnda" to "Pretty big"

[orenpa11]

Hi
Is it possible to transfer code from "intermediate student with lamnda" to 
"Pretty big"
for exmple :

(require 2htdp/image)
(require 2htdp/universe)


(define (join-together ls1 ls2)
  (local 
    [; help : [ListOf X] -> [ListOf X]
     ; (help ls1) drops the invariant argument ls2
     (define (help ls1)
       (cond
         [(empty? ls1) ls2]
         [else (cons (first ls1) 
                     (help (rest ls1)))]))]
    (help ls1)))

(check-expect (join-together '() '(a b c d e f)) '(a b c d e f))
(check-expect (join-together '(a)  '(b c d e f)) '(a b c d e f))
(check-expect (join-together '(a b)  '(c d e f)) '(a b c d e f))
(check-expect (join-together '(a b c ) '(d e f)) '(a b c d e f))
(check-expect (join-together '(a b c d)  '(e f)) '(a b c d e f))
(check-expect (join-together '(a b c d e)  '(f)) '(a b c d e f))
(check-expect (join-together '(a b c d e f) '()) '(a b c d e f))



Thanks,
Or

p.s. I get the error

check-expect: undefined;
 cannot reference an identifier before its definition

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