[Dune] YaspGrid vertex neighbour

[Aleksejs Fomins]

Dear Dune,

We have recently started using YaspGrid for another project of ours.

Hence a beginner's question:

We want to write a vertex-based code, so it feels natural to iterate over the vertices of the grid (no local grid refinement).
What is the easiest way to access neighbouring vertices of a given vertex (aka left, right, front, back, top, bottom)?

Best regards,
Aleksejs