anchor.diff:  
   ;; executes against game when drop-counter hits zero
   (defun drop-block-one (game)
  -  (declare (optimize (debug 3)))
     (let* ((fb (@ game :fb))
            (dropped-fb (with fb :y (1+ (@ fb :y)))))
       (if (legal-block-position game dropped-fb)
  
positive.code:   (@ (@ grid :v) (+ x (* y (@ grid :width)))))
  
  (defun do-grid-fun-aux (grid val fn x y width)
    (declare (optimize (debug 3)))
     (let ((v (@ grid :v)))
       (if (>= y (@ grid :height))
         val
  
negative.code: 
  ;; main is a grid hash, other is a grid hash
  (defun grid-combine-fun (main other offset-x offset-y)
    (let ((w (@ main :width))
          (h (@ main :height)))
      (with main :v
  