anchor.diff:    (sort (graph-nodes graph) #'> :key (lambda (node) (degree node graph))))
   
   (defun color (graph &aux (res (mapcar #'list (graph-nodes graph))) (counter 0))
  -  "Return alist representing a proper coloring of the vertices of the given graph, colors represented as a positive integer."
  +  "Return alist representing a proper coloring of the nodes of the given graph, colors represented as a positive integer."
     (labels ((new-color () (incf counter)))
       ;; Welsh-Powell algorithm
       (do ((nodes (sorted-nodes graph))
  
positive.code:                      (and (not (or (edge node n graph) (edge n node graph)))
                            (rplacd (assoc n res) color)))
            nodes))))
  
negative.code:                              (degree (remove start (nodes e)) graph2))))
                     edges)))
  
  ;;; p86
  
  (defun degree (node graph)
    "Return the degree of node in graph."
  