(prefix ((: <http://example/>))
  (sequence
    (join
      (bgp (?x :p ?v))
      (bgp (?x :q ?v)))
    (join
      (bgp (?x :p ?v))
      (filter ?v 
	(bgp (?y :q ?z))))
    (join
      (bgp (?x :p ?v))
      (filter ?v 
	(bgp (?y :q ?v))))
    ))