anchor.diff:    (assert-equal (vowels-to-xs "Astronomy") "xstrxnxmy")
     (let* ((subjects '("Astronomy" "Biology" "Chemistry" "Linguistics"))
            (mc-result (mapcar #'vowels-to-xs subjects)))
  -    (assert-equal mc-result ____)))
  +    (assert-equal mc-result '("xstrxnxmy" "Bxxlxgy" "Chxmxstry" "Lxngxxstxcs"))))
   
   
   ;; ----
   
   (define-test test-mapcar-with-lambda
       (let ((mc-result (mapcar (lambda (x) (mod x 10)) '(21 152 403 14))))
  -      (assert-equal mc-result ____)))
  +      (assert-equal mc-result '(1 2 3 4))))
  
positive.code:     "dotimes establishes a local lexical binding which may shadow
       a global value."
    (dotimes (*x* 4)
      (true-or-false? ___ (equal "global" *x*)))
    (true-or-false? ___ (equal "global" *x*)))
  
  
  (define-test test-loop-until-return
  
negative.code:       binding them in order to your selected symbol."
      (let ((out-list nil))
        (dotimes (y 3) (push y out-list))
        (assert-equal out-list '(2 1 0))))
  
  
  (defvar *x* "global")
  