# From Cubes to Twisted Cubes via Graph Morphisms in Type Theory

## TL;DR

This paper introduces twisted cubes in type theory, extending cube categories to model non-invertible equalities, bridging properties of cubes, globes, and simplices for higher categorical structures.

## Contribution

It develops a new category of twisted cubes by modifying the BCH cube category, enabling the modeling of directed type theories with non-invertible equalities.

## Key findings

- Defined the category of twisted cubes.
- Proved initial properties of twisted cubes.
- Showed potential to unify properties of cubes, globes, and simplices.

## Abstract

Cube categories are used to encode higher-dimensional categorical structures. They have recently gained significant attention in the community of homotopy type theory and univalent foundations, where types carry the structure of such higher groupoids. Bezem, Coquand, and Huber have presented a constructive model of univalence using a specific cube category, which we call the BCH category. The higher categories encoded with the BCH category have the property that all morphisms are invertible, mirroring the fact that equality is symmetric. This might not always be desirable: the field of directed type theory considers a notion of equality that is not necessarily invertible. This motivates us to suggest a category of twisted cubes which avoids built-in invertibility. Our strategy is to first develop several alternative (but equivalent) presentations of the BCH category using morphisms between suitably defined graphs. Starting from there, a minor modification allows us to define our category of twisted cubes. We prove several first results about this category, and our work suggests that twisted cubes combine properties of cubes with properties of globes and simplices (tetrahedra).