Project(Extend(AggregationJoin(Aggregation(??agg1: *, COUNT,
                                           {},
                                           G1=Group((?s),
                                              Filter("false"^^<http://www.w3.org/2001/XMLSchema#boolean>,
                                              BGP( ?s ?p ?o))))),
               ?C2,
               ??agg1),
        {?C2})