anchor.diff:  
   (defun format-number (event-name n)
     (when (eql n -1)
  -    (return-from format-number ""))
  +    (return-from format-number "-"))
     (case event-name
       ((:time :real-time :user-time :system-time)
          (cond ((zerop n) "0")
  
positive.code: 
  (defun report-ascertainableness (results)
    (format t "~2&")
    (let ((widths '(30 13 13 13)))
      (print-table-line widths '("" "non-GC" "GC" "Total")
                        :pad-first-column nil)
      (print-horizontal-separator widths)
      (dolist (result results)
        (destructuring-bind (event total mutator gc) result
          (print-table-line
           widths (cons (concatenate 'string
                                     (event-description-or-name event 30) ":")
                        (mapcar (lambda (x) (format-number (event-name event) x))
                                (list mutator gc total)))
           :align-first-column :right
           :pad-first-column nil))))
    (terpri))
  
  (defmacro ascertain (form &key (events '(:papi-tot-cyc :real-time
                                           :user-time :system-time)))
    `(call-with-measurements
      ,events (lambda () ,form) #'report-ascertainableness))
  
negative.code:         (pop results))
        (munge-sample-results events results))))
  
  (defun sample (function &key (events (default-events)) (samples 10) (report :table)
                 (discard-first t))
    (let ((results (%sample events function samples discard-first)))
      (ecase report
  