anchor.diff:  If no such node exists, returns NIL."
     (check-type node node)
     (check-type property-name property-name)
  -  (cdr (assoc property-name (node-transitions node) :test 'eq)))
  +  (cdr (assoc property-name (%node-transitions node) :test 'eq)))
   
   (defun find-node-by-transitions (start-node goal-properties)
     "Searches the transition tree from START-NODE to find the node containing
  
positive.code:   (sub-molds nil)
    initial-node)
  
  (defstruct (node (:predicate nodep))
    "Transitions are auxiliary data structures for molds, storing information
  about an object's direct properties. Objects keep a reference to their
  current transition as an entry point to the mold datastructure."
  
negative.code: ;;;   all sub-molds must be alerted (and they must alert -their- sub-molds), and each sub-mold must
  ;;;   recalculate its hierarchy list.
  
  (defstruct (mold (:predicate moldp) (:conc-name %mold-)
                   (:constructor
                    %make-mold (parents &aux (hierarchy (compute-hierarchy parents)))))
    "Also known as 'backend classes', molds are hidden caches which enable
  Sheeple to use class-based optimizations yet keep its dynamic power."
    (parents   nil :read-only t)
  