anchor.diff:      ((:false :true)
        (get-instance-node graph "Boolean"))
       (:null
  -     (get-instance-node graph "null"))
  +     (get-location-node graph "null"))
       (:undefined
  -     (get-instance-node graph "undefined"))))
  +     (get-location-node graph "undefined"))))
   
   (defmethod populate-nodes (graph (elm binary-operator))
     (let ((left-node (populate-nodes graph (binary-operator-left-arg elm)))
  
positive.code:     ((:false :true)
       (get-exemplar-value-nodes graph "Boolean"))
      (:null
       (get-exemplar-value-nodes graph "null"))
      (:undefined
       (get-exemplar-value-nodes graph "undefined"))))
  
  (defmethod compute-types ((elm property-access) graph)
    (let ((target-types (compute-types (property-access-target elm) graph))
  
negative.code:         for idx upfrom 0
          when (and (numberp env-min)
                    (>= idx env-min))
          do (add-assignment-edge param (get-location-node graph "undefined" queue) queue))
  
    ;; Link corresponding arguments and parameters
    ;; TODO Deal with worse-than-quadratic nature of this operation, perhaps
  