;;Chapter 3, Test 5, Page 40
(deftest test-trees ()
  (let ((lst (list 1 (list 2 4) 5)))  ;assigns lst to be a list that looks like (1 (2 4) 5
    (check
      (equal (subst 3 2 lst) '(1 (3 4) 5))  ;this replaces 2 with 3 (using subst, which is recursive), and will return the new list
      (not (equal (substitute 3 2 lst) `(1 (3 4) 5))))))  ;this shows that substitute is not recursive.