anchor.diff:    (check-type property-name property-name)
     (or (find-transition mold property-name)
         (aprog1 (make-mold (mold-lineage mold)
  -                         (hv-cons property-name (mold-properties mold)))
  +                         (hv-cons property-name (mold-properties mold)) mold)
           (aconsf (mold-transitions mold) property-name (make-weak-pointer it)))))
   
   (defun ensure-mold (parents &optional (properties #()))
  
positive.code: 
  (defstruct (mold
               (:predicate moldp)
               (:constructor make-mold (lineage properties)))
    "Also known as 'backend classes', molds are hidden caches which enable
  Sheeple to use class-based optimizations yet keep its dynamic power."
    (lineage     nil :read-only t :type lineage) ; A common cache of parent stuff
    (properties  nil :read-only t
                     :type (or simple-vector hash-table)) ; Direct properties
  
negative.code: ;;;
  ;;; Molds
  ;;;
  (defvar *molds* (make-weak-hash-table :test 'equal :weakness :value)
    "Maps parent lists to their corresponding molds. This is the global entry
  point to Sheeple's backend class system.")
  
  