Readings shared May 4, 2026

The readings shared in Bluesky on 4 May 2026 are: Compfiles: Catalog of math problems formalized in Lean. ~ David Renshaw et als. #LeanProver #ITP #Math Primitive pythagorean triples in lean and redu

Delooping generated groups in homotopy type theory

Homotopy type theory is a logical setting based on Martin-Löf type theory in which one can perform geometric constructions and proofs in a synthetic way. Namely, types can be interpreted as spaces (up to continuous deformation) and proofs as homotopy invariant constructions. In this context, the loop spaces of types with a distinguished element (more precisely, pointed connected groupoids), provide a natural representation of groups, what we call here internal groups. The construction which internalizes a given group is called delooping, because it is a formal inverse to the loop space operator. As we recall in the article, this delooping operation has a concrete definition for any group G given by the type of G-torsors. Those are particular sets together with an action of G, which means that they come equipped with an endomorphism for every element of G. We show that, when a generating set is known for the group, we can construct a smaller representation of the type of G-torsors, using the fact that we only need automorphisms for the elements of the generating set. We thus obtain a concise definition of (internal) groups in homotopy type theory, which can be useful to define deloopings without resorting to higher inductive types, or to perform computations on those. We also investigate an abstract construction for the Cayley group of a generated group. Most of the developments performed in the article have been formalized using the cubical version of the Agda proof assistant.

Readings shared April 29, 2026

The readings shared in Bluesky on 29 April 2026 are: A Lean companion to «Conceptual mathematics». ~ David Kinkead. #LeanProver #ITP #Math A milestone in formalization: The sphere packing problem in

Types and Neural Networks