[plt-scheme] Doubt Exercise 14.2.2 HTDP

Hi! I am Renato from Brazil. I am studying the 'How to Design Programs'.
In the Section 14  more specifically in the exercise 14.2.2 I have a doubt despite my tests are all passing.
While searching for a element on the binary tree, using the function Boolean?, my recursive function (search-bt) does one more
search than it should. (lines 49 - 54) Is there a better way???

Thanks!
Dutra Luciano, Renato. 
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