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In generic realizability for set theories, realizers treat unbounded quantifiers generically. To this form of realizability, we add another layer of extensionality by requiring that realizers ought to act extensionally on realizers, giving rise to a realizability universe $mathrm{V_{ex}}(A)$ in which the axiom of choice in all finite types ${sf AC}_{{sf FT}}$ is realized, where $A$ stands for an arbitrary partial combinatory algebra. This construction furnishes inner models of many set theories that additionally validate ${sf AC}_{{sf FT}}$, in particular it provides a self-validating semantics for $sf CZF$ (Constructive Zermelo-Fraenkel set theory) and $sf IZF$ (Intuitionistic Zermelo-Fraenkel set theory). One can also add large set axioms and many other principles.
Goodmans theorem (1976) states that intuitionistic finite-type arithmetic plus the axiom of choice plus the axiom of relativized dependent choice is conservative over Heyting arithmetic. The same result applies to the extensional variant. This is due
This is a short introductory course to Set Theory, based on axioms of von Neumann--Bernays--Godel (briefly NBG). The text can be used as a base for a lecture course in Foundations of Mathematics, and contains a reasonable minimum which a good (post-g
We first show that in the function realizability topos every metric space is separable, and every object with decidable equality is countable. More generally, working with synthetic topology, every $T_0$-space is separable and every discrete space is
In this paper we prove that Neutrosophic Set (NS) is an extension of Intuitionistic Fuzzy Set (IFS) no matter if the sum of single-valued neutrosophic components is < 1, or > 1, or = 1. For the case when the sum of components is 1 (as in IFS), after
Descriptive set theory was originally developed on Polish spaces. It was later extended to $omega$-continuous domains [Selivanov 2004] and recently to quasi-Polish spaces [de Brecht 2013]. All these spaces are countably-based. Extending descriptive s