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arXiv · 2005.00260

Partial Univalence in n-truncated Type Theory

Christian Sattler·Andrea Vezzosi
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Abstract

It is well known that univalence is incompatible with uniqueness of identity proofs (UIP), the axiom that all types are h-sets. This is due to finite h-sets having non-trivial automorphisms as soon as they are not h-propositions. A natural question is then whether univalence restricted to h-propositions is compatible with UIP. We answer this affirmatively by constructing a model where types are elements of a closed universe defined as a higher inductive type in homotopy type theory. This universe has a path constructor for simultaneous "partial" univalent completion, i.e., restricted to h-propositions. More generally, we show that univalence restricted to $(n-1)$-types is consistent with the assumption that all types are $n$-truncated. Moreover we parametrize our construction by a suitably well-behaved container, to abstract from a concrete choice of type formers for the universe.

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Christian Sattler, Andrea Vezzosi. 2020-05-01. Partial Univalence in n-truncated Type Theory. https://arxiv.org/abs/2005.00260

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