(define (pre-order tree)
(cond ((null? tree) '())
(else (print (entry tree))
(pre-order (left-branch tree))
(pre-order (right-branch tree)) )))
(define (in-order tree)
(cond ((null? tree) '())
(else (in-order (left-branch tree))
(print (entry tree))
(in-order (right-branch tree)) )))
(define (post-order tree)
(cond ((null? tree) '())
(else (post-order (left-branch tree))
(post-order (right-branch tree))
(print (entry tree)) )))