anchor.diff:     'weak-pointer
      'weak-pointer-p))
   
  +(declaim (inline weak-pointer-p))
   (defun weak-pointer-p (object)
     (%object-of-type-p object +object-tag-weak-pointer+))
   
  
positive.code: 
  (defun weak-pointer-live-p (weak-pointer)
    "Returns true if the weak pointer is still live."
    (logbitp +weak-pointer-header-livep+ (%object-header-data weak-pointer)))
  
  (defun examine-weak-pointer-key (key)
  
negative.code:   "Returns the key and T if the key is still live, otherwise NIL and NIL."
    (check-type weak-pointer weak-pointer)
    ;; Make a strong reference to key first.
    ;; It'll be set to NIL if the weak pointer is dead.
    (let ((key (%object-ref-t weak-pointer +weak-pointer-key+)))
      ;; Inspect the livep header bit.
      (if (logbitp +weak-pointer-header-livep+ (%object-header-data weak-pointer))
  