anchor.diff:    (signal-not-implemented 'make-atomic-integer))
   
   (defun atomic-integer-cas (atomic-integer old new)
  +  "If the current value of `ATOMIC-INTEGER` is equal to `OLD`, replace
  +it with `NEW`.
  +
  +Returns T if the replacement was successful, otherwise NIL."
     (declare (type atomic-integer atomic-integer)
              (type %atomic-integer-value old new)
              (optimize (safety 0) (speed 3)))
  
positive.code:     (incf (atomic-integer-cell atomic-integer) delta)))
  
  (defun atomic-integer-value (atomic-integer)
    (declare (type atomic-integer atomic-integer)
             (optimize (safety 0) (speed 3)))
    #-clisp
  
negative.code:       (t nil))))
  
  (defun atomic-integer-decf (atomic-integer &optional (delta 1))
    "Decrements the value of `ATOMIC-INTEGER` by `DELTA`.
  
  Returns the new value of `ATOMIC-INTEGER`."
    (declare (type atomic-integer atomic-integer)
             (type %atomic-integer-value delta)
             (optimize (safety 0) (speed 3)))
  