#| BEGIN (Write your solution here) |#
(define (lookup given-key set-of-records)
    (if (null? set-of-records) #f
        (let ((x (key (entry set-of-records))))
            (cond ((> x given-key) (lookup given-key (left-branch set-of-records)))
                ((< x given-key) (lookup given-key (right-branch set-of-records)))
                (else (key set-of-records))
            )
        )
    )
)
#| END |#