anchor.diff:                                       (object t))
     (make-instance 'cl-dot:node
       :attributes (ematch object
  -                  ((leaf c) `(:label ,c :shape :ellipse))
  -                  ((node v) `(:label ,v :shape :box)))))
  +                  ((leaf c) `(:label ,(if c "⊤" "⊥") :shape :square))
  +                  ((node v) `(:label ,v :shape :circle)))))
   
   (defmethod cl-dot:graph-object-points-to ((graph (eql 'zdd))
                                             (object t))
  
positive.code: 
  (with-zdd
    (enumerate
      (zdd-join (zdd-family '(1 2) '(7 8) '())
                (zdd-family '(1 5 9) nil)
                (zdd-set '(1)))))
  
  (with-zdd
    (enumerate
      (zdd-meet (zdd-family '(1 2) '(1 6))
                (zdd-family '(2)))))
  
  
negative.code: 
  
  ;;;; ZDDs ---------------------------------------------------------------------
  (defparameter *cache*
    (tg:make-weak-hash-table :weakness :value :test #'equalp))
  
  
  (defmacro with-zdd (&body body)
  