Project(Filter(exists((select, (bgp, (triple, <http://www.example.org/b>, <http://www.example.org/p>, <http://www.example.org/b>)), ((?x, <http://www.example.org/d>)))) ,
               BGP( ?x <http://www.example.org/p> <http://www.example.org/b>)),
        {?x})