I agree with your understanding Fergus. The best way to describe this geometry in a consistent manner for all pieces, remains to consider a4 and 4 (or h5 and 5) as a double cell. A piece on this double cell can be seen as being on both. Then, the diagram drawn by H.G. is fully correct.
I agree with your understanding Fergus. The best way to describe this geometry in a consistent manner for all pieces, remains to consider a4 and 4 (or h5 and 5) as a double cell. A piece on this double cell can be seen as being on both. Then, the diagram drawn by H.G. is fully correct.