Thanks Malone, it was as I first thought, although I missed the definition, having read it a dozen times. (Should have gone to Spec Savers). What held me up the most was the 5 answer to 5a, where I had N rather than C, which still makes more sense to me, so the definition for the decagon I had as 32 cells. I had to go through every answer again until I found it. Then, of course, I could expand the shape.