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:       (loop
          (incf loop-counter)
          (if (>= loop-counter 100) (return loop-counter)))
        (assert-equal ___ loop-counter)))
  
  
  (define-test test-mapcar
      "mapcar takes a list and a function.  It returns a new list
       with the function applied to each element of the input"
    (let ((mc-result (mapcar #'evenp '(1 2 3 4 5))))
      (assert-equal mc-result ____)))
  
  
  ;; ----
  
negative.code:       (if (> one-prime biggest-in-list)
            (setf biggest-in-list one-prime))
        (incf how-many-in-list))
      (assert-equal 4 how-many-in-list)
      (assert-equal 999565999 biggest-in-list))
    (let ((sum 0))
      "write your own dolist here to calculate the sum of some-primes"
      "you may be interested in investigating the 'incf' function"
      (dolist (prime some-primes)
        (setf sum (+ sum prime)))
      (assert-equal 999607602 sum)))
  
  
  