code: private static Boolean hasMembershipProps(final Map<IRI, Long> data) {
          return data.containsKey(LDP.membershipResource) &&
              data.getOrDefault(LDP.hasMemberRelation, 0L) + data.getOrDefault(LDP.isMemberOfRelation, 0L) == 1L;
      }
docs: Verify that ldp:membershipResource and one of ldp:hasMemberRelation or ldp:isMemberOfRelation is present