### The HoTT Effect

#### Posted by David Corfield

Martin-Löf type theory has been around for years, as have category theory, topos theory and homotopy theory. Bundle them all together within the package of homotopy type theory, and philosophy suddenly takes a lot more interest.

If you’re looking for places to go to hear about this new interest, you are spoilt for choice:

- CFA: Foundations of Mathematical Structuralism, Munich, 12-14 October 2016 (see below for a call for papers).
- FOMUS, Foundations of Mathematics: Univalent foundations and set theory, Bielefeld, 18-23 July 2016.
- Homotopy Type Theory in Logic, Metaphysics and Philosophy of Physics, Bristol, 13-15 September 2016.

For an event which delves back also to pre-HoTT days, try my

- Type Theory and Philosophy, Canterbury, 9-10 June 2016.

**CFA: Foundations of Mathematical Structuralism**

12-14 October 2016, Munich Center for Mathematical Philosophy, LMU Munich

In the course of the last century, different general frameworks for the foundations of mathematics have been investigated. The orthodox approach to foundations interprets mathematics in the universe of sets. More recently, however, there have been other developments that call into question the whole method of set theory as a foundational discipline. Category-theoretic methods that focus on structural relationships and structure-preserving mappings between mathematical objects, rather than on the objects themselves, have been in play since the early 1960s. But in the last few years they have found clarification and expression through the development of homotopy type theory. This represents a fascinating development in the philosophy of mathematics, where category-theoretic structural methods are combined with type theory to produce a foundation that accounts for the structural aspects of mathematical practice. We are now at a point where the notion of mathematical structure can be elucidated more clearly and its role in the foundations of mathematics can be explored more fruitfully.

The main objective of the conference is to reevaluate the different perspectives on mathematical structuralism in the foundations of mathematics and in mathematical practice. To do this, the conference will explore the following research questions: Does mathematical structuralism offer a philosophically viable foundation for modern mathematics? What role do key notions such as structural abstraction, invariance, dependence, or structural identity play in the different theories of structuralism? To what degree does mathematical structuralism as a philosophical position describe actual mathematical practice? Does category theory or homotopy type theory provide a fully structural account for mathematics?

**Confirmed Speakers:**

- Prof. Steve Awodey (Carnegie Mellon University)
- Dr. Jessica Carter (University of Southern Denmark)
- Prof. Gerhard Heinzmann (Université de Lorraine)
- Prof. Geoffrey Hellman (University of Minnesota)
- Prof. James Ladyman (University of Bristol)
- Prof. Elaine Landry (UC Davis)
- Prof. Hannes Leitgeb (LMU Munich)
- Dr. Mary Leng (University of York)
- Prof. Øystein Linnebo (University of Oslo)
- Prof. Erich Reck (UC Riverside)

**Call for Abstracts:**

We invite the submission of abstracts on topics related to mathematical structuralism for presentation at the conference. Abstracts should include a title, a brief abstract (up to 100 words), and a full abstract (up to 1000 words), blinded for peer review. Authors should send their abstracts (in pdf format), together with their name, institutional affiliation and current position to mathematicalstructuralism2016@lrz.uni-muenchen.de. We will select up to five submissions for presentation at the conference. The conference language is English.

**Dates and Deadlines:**

- Submission deadline: 30 June, 2016
- Notification of acceptance: 31 July, 2016
- Registration deadline: 1 October, 2016
- Conference: 12 - 14 October, 2016

## Re: The HoTT Effect

I have a somewhat jaded view of the burst of popularity of homotopy type theory within mathematics, even though it’s a good thing overall.

But I feel better about what this burst of popularity might do to philosophy. The philosophy of mathematics, unlike mathematics itself, has been stuck in contemplating old ideas on logic for far too long. (I don’t need to tell

youthat.) If more philosophers start trying to learn homotopy type theory, a bunch are bound to learn about homotopy theory, topos theory, $n$-category theory, and other branches of math that have profound new things to say about concepts like equality, numbers, propositions, logical operations, space and the like… where ‘new’ means post-1950s. This could really enliven the conversation in philosophy.