anchor.diff:  
   (defun search-node-is-dot (searchnode map-tree width treedepth)
     (member
  -    (map-tree-lookup (car (car searchnode))
  -                     (cdr (car searchnode))
  +    (map-tree-lookup (car (car (cdr searchnode)))
  +                     (cdr (car (cdr searchnode)))
                        map-tree
                        width
                        treedepth)
  
positive.code: (defun ids-path-to-pill (x y map-tree width treedepth)
      (ids 1             ;; could also start with bigger search for speed
                         ;; (at the expense of accuracy, of course)
           (cons (cons (cons x y) 0) 0) ;; search node in list
           0
           map-tree width treedepth))
  
  
negative.code:                         0)))) )
  
  (defun build-search-node ()
    (cons 0 (cons (cons 1 1) 0)))
  
  (defun build-demo-world ()
    (cons (build-map)
  