On Homotopy of Walks and Spherical Maps in Homotopy Type Theory
This article presents a refinement of one characterisation of embeddings in the sphere, called spherical maps, of connected and directed multigraphs with discrete node sets.
A combinatorial notion of homotopy for walks and the normalform of walks under a reduction relation is introduced.
The first characterisation of spherical maps states that a graph can be embedded in the sphere if any pair of walks with the same endpoints are merely walk-homotopic.
The refinement of this definition filters out any walk with inner cycles.