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