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(define (exptr b n) (cond ((= n 0) 1) ((= n 1) b) (else (iter 1 b n)))) (define (iter a b n) (cond ((= n 2) (* a (sqr b))) ((even? n) (iter a (sqr b) (/ n 2))) (else (iter (* a b) b (- n 1))))) (define (sqr x) (* x x)) (exptr 3 7)

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