def get_cts_property(self, prop, lang=None):
        """ Set given property in CTS Namespace

        .. example::
            collection.get_cts_property("groupname", "eng")

        :param prop: Property to get (Without namespace)
        :param lang: Language to get for given value
        :return: Value or default if lang is set, else whole set of values
        :rtype: dict or Literal
        """
        x = {
            obj.language: obj for obj in self.metadata.get(RDF_NAMESPACES.CTS.term(prop))
        }
        if lang is not None:
            if lang in x:
                return x[lang]
            return next(x.values())
        return x