#| BEGIN (Введите свое решение) |#
(define (lookup given-key set-of-records)
  (cond ((null? set-of-records) #f)
        ((= given-key (key (entry set-of-records))) (entry set-of-records))
        ((< given-key (key (entry set-of-records)))
         (lookup given-key (left-branch set-of-records)))
        ((> given-key (key (entry set-of-records)))
         (lookup given-key (right-branch set-of-records)))))
#| END |#