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Crossposting note: This is a crosspost from a question I first asked in MathOverflow.

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Perhaps one of the biggest issues when carrying out research in category theory is managing large amounts of data, e.g.:

Recently I've been thinking more and more about how we might be able to employ computer-assisted tools in facilitating this process, and that perhaps we may only be able to carry out certain programs with the assistance of such tools.

A concrete example might be Johnson–Gurski–Osorno's program, aiming to find categorical models for low-dimensional truncations of the sphere spectrum. For instance, in the $n=2$ case, described here, we can directly see how $\pi_{1}(\mathbb{S})=\mathbb{Z}_{/2}$ and $\pi_{2}(\mathbb{S})=\mathbb{Z}_{/2}$ arise from considering homotopy-coherent invertibility. I've always been amazed by the fact that invertibility + homotopy coherence can recover a structure as complicated as the sphere spectrum, and seeing how this goes for $n=3$ — where the wonders of $\pi_{3}(\mathbb{S})=\mathbb{Z}_{/24}$ lie — would be beyond incredible. However, the $n=2$ case already takes place at the setting of symmetric monoidal bicategories, so the average diagram looks more or less like this:

Considering that the move from $n=2$ to $n=3$ represents an increase of complexity just as big as the move from $n=1$ (i.e. the usual friendly monoidal categories) to $n=2$, one might wonder whether carrying out this program to $n=3$ would be feasible at all — at least without the use of computer tools, that is.

At its core, the problem is conceptually simple: for instance, one could view the proof that “precomposing a dinatural transformation by a natural transformation gives a dinatural transformation again” as a special case of string rewriting with 3 rewriting steps:

One could imagine a naive implementation of such a tool as follows:

  1. First, one specifies a number of rewriting rules such as “naturality”, “associativity”, “preservation of composition for functors”, etc.
  2. Second, the program accepts two strings of morphisms, which we aim to prove are equal.
  3. Then, the program tries to rewrite one string into another using the valid rewriting rules it has at hand (either purely symbolically or neuro-symbolically via deep learning).

Question. What efforts have there been trying to pursue something like this? In particular, have there been attempts hoping to augment symbolic methods (e.g. some Lean tactics) with deep learning¹?

¹I specifically mention deep learning because I think it might help at solving the resulting combinatorial explosion that happens as one starts to consider more and more involved diagram and proof steps.

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The CoREACT research project in France covers a numbers of topics around category theory, but as far as I understand automatic diagram rewriting is one of its core objective. You can find plenty of pointers on the project's website, but the people to look at more specifically given your interest are probably Nicolas Behr and Manuel Catz (his PhD student).

Not directly dealing with automation specifically, but more generally with graphical/diagrammatic reasoning in proof assistants, published work I know of (more or less in the context of CoREACT) include Ambroise Lafont's and Luc Chabassier's PhD thesis.

Re your last point, rewriting at scale is something the symbolic methods community has been doing successfully for decades, and without terrible issues with combinatorial explosion. Basically, as long as the rewriting relation is confluent, which it usually is, you are fine. For instance the kernels of proof assistants do crazy amount of rewriting all over the place, and this is far from being a performance bottleneck. In fact, so-called "proofs by reflection", which turn a proof obligation into mere computation/rewriting, are amongst the fastest/most scalable proof techniques out there (see in particular the work of Jason Gross).

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  • $\begingroup$ This is very illuminating, thank you! $\endgroup$ Commented Nov 14 at 20:01
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I am aware of:

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  • $\begingroup$ Hi Andrej, thanks for the references! I wasn't aware of the article by Guillemet–Mahboubi–Piquerez, which seems very nice! $\endgroup$ Commented Nov 13 at 22:59

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