anchor.diff:  					   x)
   				 (pushnew y (df x) :test #'eq))))))
   	(traverse start-node)))
  -    (incf *df2-call-count*)
  -    (incf *df2-run-time* (- (get-internal-run-time) time))
  -    (incf *df2-node-count* (hash-table-size result))
       result))
   
   (defun dominance-frontier (dominance-frontiers node)
  
positive.code: ;;;
  ;;; For each node in the graph, compute its dominance frontier.
  
  (defparameter *df2-call-count* 0)
  (defparameter *df2-node-count* 0)
  (defparameter *df2-run-time* 0)
  
  ;;; Compute a hash table that maps every node in a dominance tree to a
  ;;; list of its children in that tree.
  (defun children (dominance-tree)
  
negative.code: ;;; for each node.  To client code, the object returned is opaque, and
  ;;; can be used to pass to the function DOMINANCE-FRONTIER.
  (defun dominance-frontiers (start-node successor-fun)
    (let* ((dominance-tree (dominance-tree start-node successor-fun))
  	 (children (children dominance-tree))
  	 (result (make-hash-table :test #'eq)))
      (flet ((children (node)
  