<http://a.example/S1> IRI /^https?:\/\// {
   <http://a.example/p1> <http://a.example/dt1> ;
   <http://a.example/p2> BNODE {
     <http://a.example/p3> LITERAL ;
     <http://a.example/p4> IRI /^https?:\/\// @<http://a.example/S1>?
   } AND CLOSED { <http://a.example/p3> . ; <http://a.example/p4> . }
}