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2. R. Chuaqui 1980 Internal and Forcing Models for the Impredicative Theory of Classes, to appear in Dissertationes Mathematicae, vol. 176
3. P.C. Gilmore 1974 The Consistency of Partial Set Theory without Extensionality in Proceedings of Symposia in Pure Mathematics, Volume XIII, part II, American Mathematical Society, Providence, Rhode Island, 147-153.
4. The Consistency of the Axiom of Choice and of the Generalized Continuum Hypothesis with the Axioms of Set Theory;Gödel,1940