anchor.diff:         last-gen))
   
   (defun strings->char-lists (lst)
  -   (if (null lst)
  +   (if (endp lst)
          nil
          (cons (coerce (car lst) 'list) (strings->char-lists (cdr lst)))))
   
  
positive.code: ; added curx counter
  (defun build-next-generation-row (width height curx y last-gen next-gen)
     (let* ((new-tree (build-next-generation-cell width height curx y last-gen next-gen))
            (next-x (1+ curx)))
           (if (= next-x width)
               new-tree
               (build-next-generation-row width height next-x y last-gen new-tree))))
  
  (defun build-next-generation (width height cury last-gen next-gen)
     (let* ((new-tree (build-next-generation-row width height 0 cury last-gen next-gen))
            (next-y (1+ cury)))
           (if (= next-y height)
               new-tree
               (build-next-generation width height next-y last-gen new-tree))))
  
  ; Proof Pad doesn't like this because Proof Pad is buggy and doesn't like complex strings, but it works fine when compiled
  (defun avl-tree->output-line (width curx y next-gen)
     (if (< curx width)
         (string-append (if (avl-retrieve next-gen (get-avl-key curx y width)) "<td class=\"live\">&nbsp;</td>" "<td>&nbsp;</td>")
               (avl-tree->output-line width (1+ curx) y next-gen))
         nil))
  
  (defun avl-tree->output-lines (width height cury next-gen)
     (if (< cury height)
         (cons (string-append "<tr>" (string-append (avl-tree->output-line width 0 cury next-gen) "</tr>"))
               (avl-tree->output-lines width height (1+ cury) next-gen))
         nil))
  
  ;test input
  
negative.code:             (integerp width)
              (tree? last-gen)                 
              (consp input-lines))
         (if (endp (car input-lines))
             (input-lines->avl-tree 0 (1+ y) width (cdr input-lines) last-gen)
             (input-lines->avl-tree (1+ x) y width (cons (cdar input-lines) (cdr input-lines))
                                    (if (equal (car (car input-lines)) #\x)
  