 (c) Another line of objection, represented in different ways by Bernstein (Bernstein 1905), Jourdain (Jourdain 1904, 1905b) and Schoenflies (Schoenflies 1905), was that Zermelo's general operation with sets in his proof was dangerous and flirts with paradox. (See also Hallett 1984, 176–182.) In its imprecise form, the objection is that Zermelo is less than explicit about the principles he uses in 1904, and that he employs procedures which are reminiscent of those used crucially in the generation of the Burali-Forti antinomy, e.g., in showing that if the set Lγ ≠ M, then it can be extended.  (What if Lγ is already the collection W?) 