anchor.diff:  
   (defmethod variable-info ((environment entry) symbol)
     (let ((defining-info (defining-variable-info environment symbol)))
  -    (make-info environment defining-info)))
  +    (if (null defining-info)
  +	;; If DEFINING-INFO is NIL, this means that VARIABLE-INFO
  +	;; returned NIL when called with the global environment, which
  +	;; means that there was no information for this symbol.  We
  +	;; must then also respect the protocol and return nil to our
  +	;; caller.
  +	nil
  +	(make-info environment defining-info))))
   
   ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
   ;;;
  
positive.code:   (if (eq symbol (name environment))
        (make-instance 'special-variable-info
  	:name symbol
  	:identity (identity environment))
        (defining-variable-info (next environment) symbol)))
  
  (defmethod defining-variable-info ((environment symbol-macro) symbol)
  
negative.code: 
  (defmethod function-info ((environment entry) symbol)
    (let ((defining-info (defining-function-info environment symbol)))
      (if (null defining-info)
  	;; If DEFINING-INFO is NIL, this means that FUNCTION-INFO
  	;; returned NIL when called with the global environment, which
  	;; means that there was no information for this symbol.  We
  	;; must then also respect the protocol and return nil to our
  	;; caller.
  	nil
  	(make-info environment defining-info))))
  
  ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
  ;;;
  