Formulas and classes -- Axioms of Zermelo-Fraenkel -- Ordinal numbers -- Cardinal numbers -- Finite sets -- Real numbers -- Axiom of choice -- Cardinal arithmetic -- Axiom of regularity -- Transitive models -- Constructible sets -- Consistency of AC and GCH -- More on transitive models -- Ordinal definability -- Remarks on complete boolean algebras -- The method of forcing and boolean - valued models -- Independence of the continuum hypothesis and collapsing of cardinals -- Two applications of boolean-valued models in the theory of boolean algebras -- Lebesgue measurability -- Suslin's problem -- Martin's axiom -- Perfect forcing -- Remark on ordinal definability -- Independence of AC -- Fraenkel-mostowski models -- Embedding of FM models in models of ZF.