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arXiv · 2411.06636

The internal languages of univalent categories

Niels van der Weide
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Abstract

Internal language theorems are fundamental in categorical logic, since they express an equivalence between syntax and semantics. One such theorem was proven by Clairambault and Dybjer, who corrected the result originally by Seely. More specifically, they constructed a biequivalence between the bicategory of locally Cartesian closed categories and the bicategory of democratic categories with families with extensional identity types, $Σ$-types, and $Π$-types. This theorem expresses that the internal language of locally Cartesian closed categories is extensional Martin-Löf type theory with dependent sums and products. In this paper, we study the theorem by Clairambault and Dybjer for univalent categories, and we extend it to various classes of toposes, among which are $Π$-pretoposes, elementary toposes, and elementary toposes with a universe. The results in this paper have been formalized using the proof assistant Rocq and the UniMath library.

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Niels van der Weide. 2026-08-19. The internal languages of univalent categories. https://arxiv.org/abs/2411.06636

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