anchor.diff:                               (degree (remove start (nodes e)) graph2))))
                      edges)))
   
  -;; p86
  +;;; p86
   
   (defun degree (node graph)
     "Return the degree of node in graph."
  
positive.code:   (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."
    (labels ((new-color () (incf counter)))
      ;; Welsh-Powell algorithm
      (do ((nodes (sorted-nodes graph))
  
negative.code:                      (and (not (or (edge node n graph) (edge n node graph)))
                            (rplacd (assoc n res) color)))
            nodes))))
  
  ;;; p87
  
  (defun depth-traverse (graph start)
    "Traverse GRAPH depth-first, starting from START."
    (do* ((stack (list start) (cdr stack))
          (res stack)
          (node (car stack) (car stack))
          (neighbors (neighbors node graph) (neighbors node graph)))
         ((null stack) res)
         (dolist (n neighbors)
           (unless (member n res)
             ;; if not already visited, add n to stack (and thereby res)
             (rplacd stack (cons n (cdr stack)))))))
  