#
Lookup procedure
^{
}

Implement the
`lookup`

procedure for the case where the set of records is structured as a binary tree, ordered by the numerical values of the keys.

```
(define (make-tree entry left right)
(list entry left right))
(define (key entry) (car entry))
(define (entry tree) (car tree))
(define (left-branch tree) (cadr tree))
(define (right-branch tree) (caddr tree))
(define test-tree
(make-tree '(5 "Five")
(make-tree '(3 "Three")
(make-tree '(2 "Two") '() '())
(make-tree '(4 "Four") '() '()))
(make-tree '(8 "Eight") '() '())))
(check-equal? (lookup 5 test-tree) '(5 "Five"))
(check-equal? (lookup 2 test-tree) '(2 "Two"))
(check-equal? (lookup 6 test-tree) #f)
(check-equal? (lookup 8 test-tree) '(8 "Eight"))
```