(prefix ((: <http://example/>))
  (exec
    (dataset
      (default (graph
		 (:x :p 1)
		 (:x :p 2)))
      (namedgraph :g1
	(graph
	   (:x :gp 1)
	   (:x :gp 2)))
      (namedgraph :g2
	(graph
	  (:y :gp 1)
	  (:y :gp 2)))
      )

    (graph :g1
      (bgp (?x ?p ?v)))
    ))