anchor.diff:  
   
   ;;;; ZDDs ---------------------------------------------------------------------
  -(defparameter *cache* (tg:make-weak-hash-table :weakness :value :test #'equalp))
  +(defparameter *cache*
  +  (tg:make-weak-hash-table :weakness :value :test #'equalp))
   
   
   (defmacro with-zdd (&body body)
  
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:                                      (object t))
    (make-instance 'cl-dot:node
      :attributes (ematch object
                    ((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))
  