Mine

 (define (diffy-long x y) (cond ((= x 0) (display y))                                                                                                  |
|                                                                       |                            ((< y (diffy-length 1 3 7 x)) (diffy-long (- x 1) (diffy-length 1 3 7 x)))                                                 |
|                                                                       |                            ((>= y (diffy-length 1 3 7 x)) (diffy-long (- x 1) y))))                                                                   |
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|                                                                       | (define (diffy-longest) (diffy-long 1000 0))                                                                                                          |
|                                                                       | (diffy-longest)                                                                                                                                       |
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