anchor.diff:        m
       (let ((undo-list (nreverse (map-as-undo-harray--undo-list m)))
   	  (table (map-as-undo-harray--harray m)))
  -      ;(incf *map-as-undo-harray-undo-count* (length undo-list))
  -      ;(incf *map-as-undo-harray-copy-count*)
  +      ; (incf *map-as-undo-harray-undo-count* (length undo-list))
  +      ; (incf *map-as-undo-harray-copy-count*)
         (when *break-on-non-single-threaded-updates?*
   	(break "Non-single-threaded update!"))
         (let ((new-table (copy-hash-table table)))
  
positive.code: (defparameter *map-as-undo-harray-alist-elt-ref-count* 0)
  (defparameter *map-as-undo-harray-set-count* 0)
  
  (defvar *undefined* '(:|None|))
  (defun defined? (val) 
    (not (eq val *undefined*)))
  
negative.code:       ;(incf *map-as-undo-harray-set-count*)
        (let* ((last-undo-list (map-as-undo-harray--undo-list m))
  	     (old-val (gethash x table *undefined*)))
  	(if (Slang-Built-In::slang-term-equals-2 y old-val)
  	    m				; Optimize special case
  	  (progn
              (when (member table *maphash-htables* :test 'eq)
  