DCHoTT-Agda

Differential cohesion in Homotopy Type Theory by an axiomatized coreduction modality. The following is proved and could also be interpreted as theorems about general modalities:

• The formal disk bundle over a group is trivial.
• The formal disk bundle over a V-manifold is locally trivial.
• All F - fiber bundles are associated to an Aut(F) principal bundle.

In place of groups, a more general structure called homogeneous type is used in the code. Here is more information on this project. Here (theorem 3.6, 1) and some part of 2) is a short account of the question this code solves. The classical, category theoretic, version of the theory together with a lot of opportunities to extend the formalized version is here.

State of the code

Notation is not as consequent and compatible with the rest of the HoTT-World as it should be. This code grew while I was learning homotopy type theory and agda. This is still witnessed by some stupid definitions for the basic stuff like equivalences and probably some agda-clumsyness. If you want to have a look at what has been formalized, the following files are probably the right places:

• FormalDiskBundle.agda
• Manifolds.agda
• G-structure.agda
• FiberBundle.agda
• Im.agda

A Modality 'I' is defined in Im.agda in a way similar to the HoTT-Book, 7.7.5.