anchor.diff:            (multiple-value-bind (item empty-p)
                 (queue-dequeue queue)
               (unless empty-p
  -              #-deploy (assert (not (eq +empty+ item)))
  +              #+with-assertions (assert (not (eq +empty+ item)))
                 (return (values item empty-p))))
             (when (and end-time
                        (>= (get-internal-real-time) end-time))
  
positive.code: 
  
  (defun queue-empty-p (queue)
    (with-cas-retry
      (let ((head (queue-head queue)))
        (or (null head)
  
negative.code: 
  
  (defun queue-dequeue (queue)
    "Dequeue the next item from the head of QUEUE."
    (symbol-macrolet
        ((head (queue-head queue)))
      (with-cas-retry
  