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Univalence in locally cartesian closed infinity-categories

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(2012)cite http://arxiv.org/abs/1208.1749arxiv:1208.1749Comment: 26 pages. Comments are very welcome; v2: clarified some points in the introduction, minor expository changes, added one reference. No changes in theorems and proofs.

Abstract

In the setting of presentable locally cartesian closed infinity-categories, we show that univalent families, in the sense of Voevodsky, form a poset isomorphic to the poset of bounded local classes, in the sense of Lurie. It follows that every infinity-topos has a hierarchy of üniversal" univalent families, indexed by regular cardinals, and that n-topoi have univalent families classifying (n-2)-truncated maps. We show that univalent families are preserved (and detected) by right adjoints to locally cartesian localizations, and use this to exhibit certain canonical univalent families in infinity-quasitopoi (infinity-categories of "separated presheaves"). We also exhibit some more exotic examples of univalent families, illustrating that a univalent family in an n-topos need not be (n-2)-truncated, as well as some univalent families in the Morel-Voevodsky infinity-category of motivic spaces, an instance of a locally cartesian closed infinity-category which is not an n-topos for any 0 n ınfty. Lastly, we show that any presentable locally cartesian closed infinity-category is modeled by a type-theoretic model category, and conversely that the infinity-category underlying a type-theoretic model category is presentable and locally cartesian closed; moreover, univalent families in presentable locally cartesian closed infinity-categories correspond precisely to univalent fibrations in type-theoretic model categories.

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