anchor.diff:    "Maps parent lists to their corresponding molds. This is the global entry
   point to Sheeple's backend class system.")
   
  +(defun find-mold (parents)
  +  (check-list-type parents object)
  +  (values (gethash parents *molds*)))
  +
  +(defun (setf find-mold) (mold parents)
  +  (check-list-type parents object)
  +  (check-type mold mold)
  +  (setf (gethash parents *molds*) mold))
  +
   ;;;
   ;;; Transitions
   ;;;
  
positive.code:     (find-node-by-transitions it properties)))
  
  ;;;
  ;;; Creating molds
  ;;;
  (defun ensure-mold (parents)
    "Returns the mold for PARENTS, creating and caching a new one if necessary."
    (check-list-type parents object)
    (or (find-mold parents)
        (setf (find-mold parents)
              (aprog1 (make-mold parents)
                (setf (mold-initial-node it)
                      (make-node :mold it))))))
  
  (defun ensure-transition (node property-name)
    "Returns the transition from NODE indexed by PROPERTY-NAME, creating and
  
negative.code:   (check-type node node)
    (check-type property-name property-name)
    (or (find-transition node property-name)
        (aconsf (%node-transitions node) property-name
                (make-node :mold (%node-mold node)
                           :properties (cons property-name
                                             (%node-properties node))))))
  
  (defun ensure-mold (parents properties)
    (or (find-mold parents properties)
  