Bar recursion in classical realisability : dependent choice and continuum hypothesis (1502.00112v4)

Abstract: This paper is about the bar recursion operator in the context of classical realizability. After the pioneering work of Berardi, Bezem & Coquand [1], T. Streicher has shown [10], by means of their bar recursion operator, that the realizability models of ZF, obtained from usual models of $\lambda$-calculus (Scott domains, coherent spaces, . . .), satisfy the axiom of dependent choice. We give a proof of this result, using the tools of classical realizability. Moreover, we show that these realizability models satisfy the well ordering of $\mathbb{R}$ and the continuum hypothesis These formulas are therefore realized by closed $\lambda_c$-terms. This allows to obtain programs from proofs of arithmetical formulas using all these axioms.