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1 ;; Devise a correct version of the count-pairs procedure of exercise 3.16 that returns the number of distinct pairs in any structure. (Hint: Traverse the structure, maintaining an auxiliary data structure that is used to keep track of which pairs have already been counted.)3 (define (test-case actual expected)4 (newline)5 (display "Actual: ")6 (display actual)7 (newline)8 (display "Expected: ")9 (display expected)10 (newline))12 (define (count-pairs x)13 (if (not (pair? x))14 015 (+ (count-pairs (car x))16 (count-pairs (cdr x))17 1)))19 (define three '(a b c))20 (define four )21 (define seven )22 (define circular )