anchor.diff:       lexical form.  After which, the previous value, if it exists, is visible again."
     (setf a 10)
     (setf b 20)
  -  (assert-equal a ___)
  -  (assert-equal b ___)
  +  (assert-equal a 10)
  +  (assert-equal b 20)
     (let ((a 1111)
           (b 2222))
  -    (assert-equal a ___)
  -    (assert-equal b ___))
  -  (assert-equal a ___)
  -  (assert-equal b ___))
  +    (assert-equal a 1111)
  +    (assert-equal b 2222))
  +  (assert-equal a 10)
  +  (assert-equal b 20))
   
   
   (define-test test-let-default-value
       "let vars have a default value"
       (let ((x))
  -      (assert-equal ___ x)))
  +      (assert-equal 0 x)))
   
   (define-test test-let-bindings-are-parallel
       "When defining the bindings in the let form, later bindings may not depend
  
positive.code:   (setf a 100)
    (let ((a 5)
          (b (* 10 a)))
      (assert-equal b ___)))
  
  (define-test test-let*-bindings-are-series
      "let* is like let, but successive bindings may use values of previous ones"
    (setf a 100)
    (let* ((a 5)
           (b (* 10 a)))
      (assert-equal b ___))
    (assert-equal a ___))
  
  
  (define-test write-your-own-let-statement
  
negative.code: 
  (define-test test-limits-of-case
      "case is not suitable for all kinds of values, because
       it uses the function eql for comparisons. We will explore
       the implications of this in the equality-distinctions lesson"
    (let* ((name "John")
           (lastname (case name ("John" "Doe")
  