Category Archives: Univalence

Not every weakly constant function is conditionally constant

As discussed at length on the mailing list some time ago, there are several different things that one might mean by saying that a function is “constant”. Here is my preferred terminology: is constant if we have such that for … Continue reading

Posted in Univalence | 8 Comments

Splitting Idempotents

A few days ago Martin Escardo asked me “Do idempotents split in HoTT”? This post is an answer to that question.

Posted in Code, Homotopy Theory, Univalence | 12 Comments

Higher inductive-recursive univalence and type-directed definitions

In chapter 2 of the HoTT book, we prove theorems (or, in a couple of cases, assert axioms) characterizing the equality types of all the standard type formers. For instance, we have and (that’s function extensionality) and (that’s univalence). However, … Continue reading

Posted in Code, Foundations, Higher Inductive Types, Univalence | 7 Comments

Eilenberg-MacLane Spaces in HoTT

For those of you who have been waiting with bated breath to find out what happened to your favorite characters after the end of Chapter 8 of the HoTT book, there is now a new installment: Eilenberg-MacLane Spaces in Homotopy Type Theory Dan … Continue reading

Posted in Applications, Code, Higher Inductive Types, Paper, Univalence | 6 Comments

Another proof that univalence implies function extensionality

The fact, due to Voevodsky, that univalence implies function extensionality, has always been a bit mysterious to me—the proofs that I have seen have all seemed a bit non-obvious, and I have trouble re-inventing or explaining them.  Moreover, there are … Continue reading

Posted in Univalence | 4 Comments

The HoTT Book

This posting is the official announcement of The HoTT Book, or more formally: Homotopy Type Theory: Univalent Foundations of Mathematics The Univalent Foundations Program, Institute for Advanced Study The book is the result of an amazing collaboration between virtually everyone involved … Continue reading

Posted in Foundations, Higher Inductive Types, Homotopy Theory, Paper, Univalence | 3 Comments

Universe n is not an n-Type

Joint work with Christian Sattler Some time ago, at the UF Program in Princeton, I presented a proof that Universe n is not an n-type. We have now formalized that proof in Agda and want to present it here. One … Continue reading

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