A complete axiomatization of infinitary first-order intuitionistic logic over $\mathcal{L}_{\kappa^+, \kappa}$

Abstract

Given a weakly compact cardinal $\kappa$, we give an axiomatization of intuitionistic first-order logic over $\mathcal{L}_{\kappa^+, \kappa}$ and prove it is sound and complete with respect to Kripke models. As a consequence we get the disjunction and existence properties for that logic. This generalizes the work of Nadel for intuitionistic logic over $\mathcal{L}_{\omega_1, \omega}$. When $\kappa$ is a regular cardinal such that $\kappa^{<\kappa}=\kappa$, we deduce, by an easy modification of the proof, a complete axiomatization of intuitionistic first-order logic over $\mathcal{L}_{\kappa^+, \kappa, \kappa}$, the language with disjunctions of at most $\kappa$ formulas, conjunctions of less than $\kappa$ formulas and quantification on less than $\kappa$ many variables. In particular, this applies to any regular cardinal under the Generalized Continuum Hypothesis.