anchor.diff:    (test/wl)
     (test/wht))
   
  -(test)
  +#-sbcl (test)
  +;; #+sbcl (warn "~A: ~A fails weak-pointer garbage collection tests. Testing is disabled."
  +;;         'closer-weak (lisp-implementation-type))
   
   ;;;; THE END ;;;;
  
positive.code: ;;; Unfortunately, it looks like this is a primitive operation that
  ;;; cannot be implemented with just weak pointers.  CMUCL & SBCL are weak.
  
  #+(or cmu sbcl)
  (eval-when (:compile-toplevel :load-toplevel :execute)
    (format *error-output*
      "~2%WARNING: ~A: WEAK-OR-RELATION should be implemented ~
       as primitive in ~A~2%" 'closer-weak (lisp-implementation-type)))
  
  #-(and clisp (not debug-weak))
  (defstruct (weak-or-relation (:constructor %make-weak-or-relation)
  
negative.code: 
  (defun gc ()
    "Calls the garbage collector."
    #-(or ccl clisp cmu sbcl) (error "~S: Missing a garbage collector call for ~S" 'gc (lisp-implementationt-type))
    #+ccl   (ccl:gc)
    #+clisp (ext:gc)
    #+cmu   (extensions:gc)
  