Project(Lateral(BGP( ?s <http://example/p> ?o),
                Slice(Project(Extend(BGP( ?s <http://example/label> ?label),
                                     ?label_count,
                                     count(?label) ),
                              {?s, ?label_count}),
                      0,
                      2)),
        {?label_count, ?o, ?s})