sentences:  it seems therefore more correct to take an intensional view of relations, and to identify them rather with class-concepts than with classes".As shown below, Norbert Wiener (1914) reduced the notion of relation to class by his definition of an ordered pair.The outright prohibition implied by Russell's "axiom of reducibility" was roundly criticised by Ernst Zermelo in his 1908 "Investigations in the foundations of set theory I", stung as he was by a demand similar to that of Russell that came from Poincaré