 Weyl addressed the problem of generating the admissible properties over a given domain a few years later in Das Kontinuum (1918). As in 1910, the set of sets of natural numbers that are definable via admissible operations (to which now also a form of iteration is added) is denumerable. By Cantor’s argument there is no relation which parametrizes all subsets of natural numbers (Weyl 1918, section 5). Weyl apparently followed a relativistic attitude, according to which the extension of the universe of sets and their properties depend on the operations which are accepted to construct sets (see also the entry  Hermann Weyl).