anchor.diff:                             (true (cell 3 1 x)) (true (cell 3 2 o)) (true (cell 3 3 b))
                              )))
         (apply-rule-forest *r* <> (zr-possible-forest *r*))
  -      (zdd-join (make-iset *r* '((does oplayer (mark 3 3))
  -                                 (does xplayer noop))))
  +      (zdd-join <> (make-iset *r* '((does oplayer (mark 3 3))
  +                                    (does xplayer noop))))
         (apply-rule-forest *r* <> (zr-happens-forest *r*))
  -      ; (zdd-meet <> (zr-next-zdd *r*))
  +      (zdd-meet <> (zr-next-zdd *r*))
         (dump-iset *r* <>)
         (no <>)
         ; (draw-zdd *r* <>)
  
positive.code: 
  ;;;; Phase 2: Head Finalization
  (defun walk-tree-positive (rule-tree heads)
    (adt:match scully.rule-trees::rule-tree rule-tree
      ((scully.rule-trees::node term hi _)
       (if (member term heads)
         (walk-tree-positive hi heads)
         (tree-to-result rule-tree)))
      (_ (tree-to-result rule-tree))))
  
  (defun walk-stratum-positive (stratum heads)
    (iterate
  
negative.code: (defparameter *i* (initial-iset *r*))
  (defparameter *j* (initial-iset *r*))
  
  (with-zdd
    (-<> *r*
      (make-iset <>
                 '(
                   (true (control xplayer))
                   (true (cell 1 1 B)) (true (cell 1 2 x)) (true (cell 1 3 o))
                   (true (cell 2 1 B)) (true (cell 2 2 o)) (true (cell 2 3 o))
                   (true (cell 3 1 x)) (true (cell 3 2 x)) (true (cell 3 3 x))
                   ))
      (apply-rule-forest *r* <> (zr-possible-forest *r*))
      (draw-zdd *r* <>)
      (dump-iset *r* <>)
      (no <>)
      ))
  
  
  (defun test ()
    (with-zdd
      (-<>
          (zdd-union
            (make-iset *r* '(
                             (true (control oplayer))
                             (true (cell 1 1 o)) (true (cell 1 2 x)) (true (cell 1 3 x))
                             (true (cell 2 1 x)) (true (cell 2 2 o)) (true (cell 2 3 b))
                             (true (cell 3 1 x)) (true (cell 3 2 o)) (true (cell 3 3 b))
                             ))
            (make-iset *r* '(
                             (true (control oplayer))
                             (true (cell 1 1 o)) (true (cell 1 2 x)) (true (cell 1 3 x))
  