While homotopy type theory formalizes homotopy theory, it is not a priori clear – and in fact is or was an open problem – how to formalize general homotopy-coherent structures of higher algebra/higher category theory: Since these typically involve an infinite hierarchy of coherence-conditions, these cannot be axiomatized directly, but one needs some scheme that generates them. This turned out to be subtle.
Eric Finster had previously considered another variant of type theory, called opetopic type theory which natively talks about infinity-categories and their higher coherences by type-theoretically formalizing the structure of opetopic sets. In new work Finster 18 he gives something like an implementation of aspects of opetopic type theory within homotopy type theory and provides evidence that this is yields a tool to solve the general problem of coherences of higher algebra/higher category theory within homotopy type theory.
Eric Finster, Towards Higher Universal Algebra in Type Theory, Homotopy Type Theory Electronic Seminar 2018 (pdf slides, recording)
Agda code at: github.com/ericfinster/higher-alg
The idea of opetopic sets that Finster 18 is inspired by goes back to
Collecting the definitions and trying them out here. The idea is to go through the definitions in the talk and the definitions in the agda formalisation to play around with.
Definition Fix a type $I$ of sorts. A polynomial over $I$, $\Poly I$, is the data of
Remark
For $i : I$, an element $f: \Op i$ represents an operation whose output sort is $i$.
For $f : \Op i$ and $j : I$, and element $p : \Param_i(f, j)$ represents an input parameter of sort $j$.
The $\Op i$ and $\Param_i (f, j)$ are not truncated at set level. So operations and parameters can have higher homotopy.
A polynomial $P : \Poly I$ generates an assocaiated type of trees.
Definition The inductive family $\Tr P : I \to \mathcal{U}$ has constructors
For a tree $w : \Tr (P, i)$, we will need its type of leaves and type of nodes
Definition
Revision on December 7, 2018 at 09:50:30 by Urs Schreiber. See the history of this page for a list of all contributions to it.