anchor.diff:          :test #'equal))))
   
   
  -(let ((*draw-unique-sinks* nil))
  -  (with-zdd
  -    (-<> (zdd-family
  -           '(1 2 100 200 6000)
  -           '(100 200 300)
  -           '(99 100 200 300)
  -           '(1 9900)
  -           '()
  -           '(1 2 1001)
  -           )
  -      (mapprint-through #'enumerate <>)
  -      (print-through #'line <>)
  -      (zdd-match <> '() 100 999)
  -      (mapprint-through #'enumerate <>)
  -      (draw <>)
  -      (never <>)
  -      )))
  +(with-zdd
  +  (-<> (zdd-family
  +         '(1 2 100 200 6000)
  +         '(100 200 300)
  +         '(99 100 200 300)
  +         '(1 9900)
  +         '()
  +         '(1 2 1001)
  +         )
  +    (mapprint-through #'enumerate <>)
  +    (print-through #'line <>)
  +    (zdd-match <> '(100 200) 100 999)
  +    (mapprint-through #'enumerate <>)
  +    (draw <> :hexp (lambda (v) (>= 999 v 100)))
  +    (never <>)
  +    ))
  
positive.code: ;;;; GraphViz -----------------------------------------------------------------
  (setf cl-dot:*dot-path* "/usr/local/bin/dot")
  (defparameter *draw-unique-sinks* nil)
  
  (defun attrs (object &rest attributes)
    (make-instance 'cl-dot:attributed
      :object object
      :attributes attributes))
  
  (defmethod cl-dot:graph-object-node ((graph (eql 'zdd))
                                       (object node))
    (make-instance 'cl-dot:node
      :attributes (ematch object
                    ((node v) `(:label ,v :shape :circle)))))
  
  (defun sink-attrs (val)
    `(:label ,(if val "⊤" "⊥")
  
negative.code: 
  
  ;;;; Scratch ------------------------------------------------------------------
  (with-zdd
    (-<> (zdd-join (zdd-family '(1 2) '(7 8) '())
                   (zdd-family '(1 5 9) nil)
                   (zdd-set '(1)))
      (print-through #'enumerate <>)
      (zdd-keep-avoiders-of <> '(2 7))
      (print-through #'enumerate <>)
      (draw <>)
      (zdd-size <>)
      ))
  
  
  (defparameter *rules* '(
                          (1001 (not 2) 1)
  