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