anchor.diff:  
   (define-test test/set-equal (test-class)
     (flet ((test-set (&rest elements)
  -           (copy test-class elements)))
  +           (make-set test-class elements)))
       (assert-true (set-equal (test-set)
                               (test-set)))
       (assert-true (set-equal (test-set 1)
  
positive.code: 
  (define-test test/union (operator test-class)
    (flet ((test-set (&rest elements)
             (copy test-class elements)))
      (check set-equal (funcall operator
                               (test-set 1 2 3 7 8 10 11 12)
                               (test-set 1 2 3 7 8 10 11 12))
  
negative.code: 
  (define-test test/intersection (operator test-class)
    (flet ((test-set (&rest elements)
             (make-set test-class elements)))
      (check set-equal (funcall operator
                               (test-set 1 2 3 7 8 10 11 12)
                               (test-set 1 2 3 7 8 10 11 12))
  