(define my-bst (make-nonempty-tree 4 left right)) ⇒ creates the list (4 left right) (root my-bst) ⇒ 4 (left-subtree my-bst) ⇒ left (right-subtree my-bst) ⇒ right
(define root __?__) (define left-subtree __?__) (define right-subtree __?__)