code: private static boolean hasMembershipProps(final Graph graph) {
          return graph.contains(null, LDP.membershipResource, null)
                          && (graph.stream(null, LDP.hasMemberRelation, null).count()
                                          + graph.stream(null, LDP.isMemberOfRelation, null).count() == 1L);
      }
docs: Verify that ldp:membershipResource and one of ldp:hasMemberRelation or ldp:isMemberOfRelation is present